According to the use guide, makeup affects how likely a player is to attain his potential ratings, and how quickly or slowly he declines with age. It affects development raher than performance.

Here's an example of a perceived effect for what I call "natural position", albeit just one game, but it's the type of performance that makes me wonder about such things...  Hardball Dynasty – Fantasy Baseball Sim Games - Player Profile: Luther Wilson.    I picked up this pitcher in the off season as an FA to work in long relief.   My SP1 thru SP5 are all locked up with very good players... no need for a 6th starter.   So I plug this guy into my long relief thinking he is more than capable, but over the course of 16 appearances and 20 innings, he gets blown up with an era hovering around 9.00.

I understand the sample size is wayyyyyy to small and he should rebound...  but be as it may, I found my self needing a spot start vs a team with a top 5 record in the league.    Wilson goes out and throws 6 innings of shut out ball in his first start I give him.  

Again, just one game means nothing in terms of evidence.  But giving this player a chance to start has resulted in a performance that begs me to find him room to start again.   When things like this happen, it leads me to believe he MIGHT be getting some sort of fractional bonus multiplier to reward me for finding his correct role.  Starter vs. reliever.   I'll give him a few more starts and see what shakes out.

In a somewhat related item, I have also seen players respond to getting a shot at batting clean-up.    Mediocre performances all year long and then.. bam.. I shuffle the line-up and give them a chance to bat 4th and they respond with big offensive numbers.