It'd be a bit like batting Tendulkar at 3. Parker's played for a million years at 4 and been one of the best batsmen in the comp consistently; moving him would be a silly idea unless he was getting stranded or something.
Pretty much exactly this, combined with the fact that Thornton, Dempsey and Petrucci have all played rep level at #3, and yourself and Alessi have done so for us before. And I hope to god that our number four batsman isn't going to be consistently stranded.....