I mean he has to be involved in the approach play as well as being the final presence in the box, meaning you're diluting his responsibilities and using him as a complete forward.
His best role is as the most advanced player of the attacking unit, where he can spearhead the line but identify pockets of space to drop into and collect the ball so he can turn and run at defenders, instead of laying it off for the more patient build up play.
I don't think he is being asked to do any more than he was at first tbh. I think the way we're setting up is to keep his job relatively simple and keep him to the middle third of the pitch. We're looking for pacy wingers and creative players to go with our wing-backs to create the chances to finish in the box. Pienaar being the exception because he's just ace paired with Baines.
At least I hope so, because to me, his best quality above all isn't his turning running with the ball, it's his finishing and his runs into the box. Don't get me wrong, his goals against Arsenal, Hull and several goals for WBA are examples of why that's an ace ability he has, but his best feature is the way he can make an intelligent run for the winger/full back to pick him out and that if he is picked out, he's finishing it. His goals last season show it perfectly. The goals vs West Ham (h), Newcastle (h&a), Southampton, Villa, Stoke, Swansea show him making space for himself, telling the assister where he wants it and making brilliant runs that he ends up finishing superbly.
His play in the penalty area is second to almost no one in the league. If we can get cut-backs and low crosses in to him at the rate we were back when Jelavic was enjoying his purple patch, he'll score 25+ this season. I think to point to his touch and hold-up play when it's not going well is to overlook the fact that he's probably just not been getting service. We'll all forget about his hold-up play if we just give him good service.