Re: Not being challenged as Uke?
I would say first allow your tori to do the exercise and get the global flow of the technique. THen graudally add more details to focus on. One of which can be the pin. Off course when tori is (supposed to be more) advanced, your expectation can differ. But it really depends on what the focus is of tori.
But when intend is there to do a proper pin and then you feel something is wrong, I think it is your role as aite to point that out and help tori to understand where things fail.