I added in Hebrew an idea on how to answer a question in Tosphot in Bava Metzia page 14.
It is simply that Tosphot must be comparing the case of improvements with teh priceof the field.
Clearly if the first buyer is getting from the borrower then there is something that prevented the lender from getting it. Otherwise how could the lender have collected anything from the first buyer? That is what causes Tosphot to think there is something also that prevents the lender from collecting from the second field