I’ve always set them between A and B. I think setting them either up or down can add additional lift on cretin aircraft. The 4* 40 is a great airplane with plenty of lift already. I have the venture 60 which is designed by the same guy and I set mine in the middle.

Others with more knowledge might chime in with reasons to do otherwise but I’ve never had a problem setting them in the middle.

Good luck with the 4*!

Jeff