4 fans seems like overkilled, I only used one.

My guess you have 2 fan flowing toward the top and 2 blowing toward the bottom?

If your temps are 5 degrees higher on the top and you have fan flowing air toward the top shut them down.

Ideally a picture of your incubator would really be best to see how the heat is placed and where the fans are placed.

You will have a temperature differential in your incubator which is ok (I have 2 degrees differential)