To return to the issue I left off with last week, Rashbam and Tosfos disagree whether the owner of bikurim can read the parsha of viduy bikurim if the fruit is brought by a shliach. Rashbam invokes the rule of shlucho shel adam k’moso to justify the owner saying “heyveisi es pri ha’adama’. Why does Tosfos disagree?
I think the key to understanding the issue is a yesod of the Dvar Avraham touched on once before. There is a minhag to deliver mishloach manos through a shliach, and usually people ask a child to be the delivery boy. The Dvar Avraham asks why this accomplishes anything, as a katan is excluded from shlichus? The D.A. explains that where shlichus requires that the shliach be representative of the sender, a katan is excluded, as we cannot invoke shlucho shel adam k’moso, but where all that is required is delivery, even a katan can serve as a means to that end.
In our case, perhaps Tosfos would argue that the shlichus of bikurim is simply a means to the end of delivery, and not a function of shlucho shel adam k’moso. Rashbam disagrees, because the idea of ‘heyveisi’ implies the actual presence of the owner.
Once we invoke shlucho shel adam, as Ezra noted in a comment, why does having to recite 'adamah asher nasata li' preclude the shliach reading the parsha himself - isn't he the equivalent of the owner? I would suggest that shlucho shel adam k’moso can be invoked when the shliach represents the owner in performing some act; however, the parsha of viduy bikurim requires not just a delivery act, but a status of landowner, and for that shlichus is insufficient. IIRC, one cannot apply the din of ‘ba’alav imo” if a shliach of the owner if present because ‘ba’alav imo’ is a status, a state of being, not an action.