You run the risk of the stats you want (heading), not improving on a different schedule and undesirable stats going up (e.g marking) going up instead if you put him on the defender schedule.
I'd make an individual schedule just for him and take bits and pieces from the striker and defender schedules to improve the stats you want. I'm sure theres a post around here somewhere that tells you exactly what sliders improve what stats.
My own (possibly) silly question:
How do I go about choosing a formation for my team? I've analysed my team, and I seem to be strong in all areas of the pitch (5-7 stars), and with half decent backup. Does it depend on how I decide to play, or is there other things in my players I should be looking for (e.g crossing stat on my wingers)?