The thing is, Piroe's all round game has never been the best. He's a great ball striker and finisher, but he doesn't stretch a back line, he doesn't link play, and he doesn't press high. He's in the 10 because he can't press high, and being a bit deeper means he, in theory, can get more opportunities to strike from distance, which is one of his strengths. Moving him to 9 may be more effective, but the front line is so fluid, i doubt we'd notice any difference beyond where they're named on the team sheet.