Daas in Kinyanim, Shlichus, and T'naim

The Kobetz Hearos in Siman 76 asks why it is that in some things like writing a get, shechita, and chalitza we say that a koton is kosher in performing the action if a gadol is omed 'al gabav, whereas in other instances, like kinyanim, kiddushin, and gerushin we say that gadol omed al gabav doesn't help (see Tosafos in Yevamos 104b). See also the Chidushei HaGrach in Yibbum and Chalitza:4 that asks the same question.
In Tosafos (ibid) he says as far as the writing of a get that the reason gadol omed al gabav works is because it is clear that the koton knows whats going on because we see him writing the get. From this it would seem that the reason gadol omed al gabav doesn't work in other cases, like the actual gerushin etc. is because it is not clear that the koton is aware of what is happening.
R' Chaim answers with a distinction between daas and kavana. He explains that gadol omed al gabav can help for a koton to have kavana, and it is only kavana that is required in cases like chalitza or writing a get lishma. However, in an actual maaseh kinyan or maaseh gerushin/kiddushin, it is not only kavana that is needed, but daas as well. A koton can never have daas, even with a gadol omed as gabav.
It seems that this chiddush of the Grach goes hand in hand with another of the Grach's chiddushim. In the hosafos to the Chidushei HaGrach Stencils, the question of why one can't have a shliach do a mitzvah for him is raised. The opinion of the Ktzos is that mitzvos must be done specifically with the doers body and thus shlichus cannot work. The Grach argues that the reason is because shlichus only works in areas that are related to baalus. We see this in Kesuvos 74a where it says that something that a tnai works in shlichus also works in. The Grach explained that if someone can't make a tnai in something it shows he is lacking baalus, and m'maila he cannot appoint a shliach either.
Now, in that very sugya in Kesubos we find that chalitza is one of the things that one cannot make a tnai or a shliach in. Thus, it would seem that why one cannot make a shliach in chalitza would be subject to a machlokes between the Ktzos and R' Chaim. The Ktzos would say that it is specifically to be done b'gufo. R' Chaim would argue that there is no baalus involved in chalitza.
At this point, we have two separate chiddushim from the Grach within chalitza. First, that chalitza doesn't require daas. Number 2, that one has no baalus in chalitza. It would not seem such a stretch to now suggest that in reality the two concepts, daas and baalus, actually go hand in hand. Daas refers specifically to daas baalim, and one has baalus only in something that requires his daas.
In order to further clarify, we can pose the following question. When we find an area of halacha which requires one's kavana is the kavana a part of the maaseh, or a separate component. Logically it would seem that this would be dependent on whether a tnai can be made. For example, in shechita there is no inyan of kavana (see shchita 20:11). Certainly, one cannot make a tnai in shechita. If it's a kosher shechita it's kosher, it doesn't matter if you put some condition on the shechita or not.
Thus, by gerushin/kiddushin etc. a tnai works. The idea is that the kavana of the mekadesh is not part of the maaseh. Rather it is a separate component that controls the challos of the maaseh. A tnai can prevent the maaseh from being chal (as opposed to shechita where there is no challos, the maaseh was either done or it wasn't). By chalitza, a tnai doesn't work. The idea is that the kavana is a part of the maaseh chalitza. You can't make a tnai because the kavana isn't a separate component in the challos.
On this topic there is some more to investigate. For example, see Ishus 6:1 in the Kesef Mishna and Magid Mishna if we even pasken milsa d'laisa bishlichus lesa bitnai. Also, see Eretz Hatzvi Siman 25 that assumes (as we did) the reverse also, that milsa d'lesa bitnai lesa b'shlichus. However, in Stencils 93 it appeared to me that R' Chaim may not be assuming that. In that piece he seems to assume that tnai is a chiddush of the torah, and not dependent on daas.
This last point may be a machlokes rishonim. The Shut HaRosh 35:9 seems to see tnai as a chiddush of the torah. The Rashba in Gittin 74b is mashma that it's a svara peshuta that one can insert a tnai into his daas.