Usually that's the case, but Heyward has shown (through small samples) elite defence at CF. He has played it through the minors, he has played it in the regular season at times, and he has also been put into that situation in the postseason. If anything he should have been a full time CF a long time ago. Knowing that managers have relied on him to field that position though in the postseason also means that they are comfortable with him performing at a good rate, and he has shown that. Jim Edmonds was a case that was thrusted around his first couple of seasons playing RF, CF, LF, and even 1B. Sure enough he became one of the top all-round CFs during his career. Shane Victorino is another case.