Eating Matzah on Erev Pesach

The Yerushalmi in Pesachim in the beginning of the 10th perek says from R' Levy that anyone who eats matzah on Erev Pesach it is like he is boel arusaso b'beis chamav. From here we learn that on Erev Pesach one should not eat matzah. There is a machlokes rishonim as to how much of the day of erev pesach is the prohibition in effect.

On Daf 15b in Dapei HaRif of Pesachim the Baal HaMaor and the Milchamos argue about this issue. The Baal HaMaor says that the prohibition only exists from the time the issur chametz sets in 6 hours into the day of erev pesach. In other words, the prohibition to eat matzah on erev pesach is directly linked to the prohibition of chametz on erev pesach.

The Ramban argues. He holds that from the Yerushalmi it is clear that the prohibition is all day. The proof of the Ramban from the Yerushalmi isn't all that clear.

In the Yerushalmi there is another shitah brought from R' Yehudah ben Besaira who makes the statement - whether chametz or matzah one can't eat it. The Ramban says, from the fact that he said nothing about 6 hrs. into the day, it follows that the issur is all day.

The Ran (dapei harif 16a) asks on this proof. Even if we assume that this is what R' Yehuda ben Besaira meant he is still linking the issur matzah to the issur chametz. R' Yehuda ben Besaira is merely l'shitaso that chametz is also assur all day on erev pesach. We, who hold that the issur chametz is only from chatzos should apply the same issur to matzah. In other words, R' Yehuda ben Besaira is linking the issur chametz to the issur matzah, so the Ramban has no proof whatsoever.

R' Moshe in Iggros Moshe Chelek 1:155 addresses this machlokes rishonim. He is trying to determine how we should pasken. Should we be machmir like the Ramban or not?

R' Moshe makes a lengthy argument to try to show how the Yerushalmi actually fits with the Ramban. It seems to me that the thrust of his argument relies on the logic that if the tannaim don't say anything we should assume that the issur is all day. It is a much more lengthy argument though, so I don't want to oversimplify it - take a look yourself.

Then R' Moshe writes the following (rough translation):

And therefore even though the issur of matzah on erev pesach is only midrabbanan, that according to the rules of psak we that the Rema writes in Choshen Mishpat 25:2 we should go like the lenient opinion that the issur is only from the zman issur chometz, nevertheless since it has been explained that the simple pshat of the Yerushalmi is like the Ramban that it is assur all day because the explanation of the Baal HaMaor and the Ran is dochek, therefore one should be machmir like the Ramban and the Rambam acc. to the Maggid Mishneh and other Rishonim that assur all day, and as is the minhag in our countries.

This seems difficult to me. R' Moshe is ruling like the Ramban because the pashtus of the Yerushalmi is like him. But the Ran himself was talking about the same Yerushalmi and said that the Yerushalmi isn't like the Ramban. And the Baal Hamaor was also talking about the same Yerushalmi, so he also didn't think the pashtus was that way. Essentially we have rishonim arguing about what the pashtus of the Yerushalmi is. Also, R' Moshe took several columns to explain how the Yerushalmi follows the Ramban (to answer a question of the Ran), so how is that the pashtus?

On the other hand, R' Moshe does say that the minhag is to be machmir, so for that reason maybe one should be machmir.

R' Moshe also deals with the analogy to an arusah b'beis chamav. He isolates two ways of understanding the issur of arusah b'bais chamav. One is that it is the same as the issur penuyah, essentially she isn't yet your wife. The second approach is that only bias mitzvah is muttar (like for mitzvas onah or for pru urvu). In the arusah period there is no mitzvah - so m'meilah biah is assur.

In the second approach the analogy is smooth. By matzah also, we aren't at the zman mitzvas matzah yet, just the preparatory stage - so it is assur. R' Moshe points out that in the first approach it is difficult because if the issur arusah is the same as penuya - so matzah should be assur all year! Why only on erev pesach?

R' Moshe says the two derachim would actually break down into the shitas baal hamaor and Ramban. In the second approach the ides is that in a preparatory stage we assur. If so, it makes sense that all of erev pesach is considered preparatory. R' Moshe even says that 30 days before pesach it could've been assur, but the Rabbanan were meikil. He says this also explains the minhag not to eat matzah from Rosh Chodesh Nissan until Pesach.

In the first approach where the analogy isn't smooth, R' Moshe says pshat must be that we assur matzah any time that there are "dinei pesach" just like we assur an arusah who has "dinim of ishus". Thus, the issur would only be in the zman of dinei pesach - i.e. when chametz is assur.

All of this I also have a bit of difficulty with. I thought that within the analogy the Baal HaMaor's approach is surely more logical (to relate the issur matzah and the issur chametz). Why do we only assur matzah because of arusah b'bais chamav? Why not assur lulav before sukkos and sitting in the sukkah as well sukkah? And marror before Pesach? How would R' Moshe explain this? If the issur is not to do a mitzvah in the preparatory time preceding the mitzvah all these cases should also be assur.

Therefore, it would seem that the idea is that when chametz is assur you might think that matzah is now muttar. Just like an arusah, if she is now assur to other men and ishus started, one might think she is muttar to her husband. Thus, we say no. The heter to her husband is only after nissuin, and the heter for matzah is only after Pesach begins. If you tie the issur matzah into chometz it makes much more sense why the issur applies here and not to other mitzvos on erev yom tov. The issur chametz and heter matzah are related. Therefore, the Yerushalmi says no, there is a erusin period where you do not yet eat matzah.

These are some issues that I had with this Iggros Moshe. Any insights would be appreciated.