RE: Extra 300S 60 Size balance
Well this IS supposed to be a hot and sensitive aerobatic ship. Selecting a stability margin at 20% is putting the CG at what a basic trainer would fly with or maybe even further ahead than that. Most aerobatic models are going to be in at around the 5 to 0% stability margin and from there the pilots just deal with it by using lots of exponential and a very light touch on the sticks.
Just so we know are these numbers you got in terms of the MAC position compatible with the kit instructions or is the kit spec out in left field?