Agreed UC, but some coasters it does make a real difference. If there is only a short drop before the next hill, or a corner, the back can be dead for airtime as the train starts to slow as it climbs/turns if the back isn't all the way over yet. Balder is a prime example of this. The airtime at the back is often killed completely by the short dip into a turn.
I found my best run on Balder was in the middle. Likewise, I found the best runs on Boulder Dash to be a few rows back where maybe you're maximising the amount of constant speed across the hill?
I do find mood makes a difference too. I love the feeling of being "pulled" or "whipped" over the top of a hill you get from the back, but sometimes I enjoy the feeling of being pushed over which gives that more sustained kind of floater.
I think the hill shape has a lot to do with it as well, which can vary a lot on wooden coasters, especially older ones where there was less "refined physics" involved in the engineering.