The plane I'm building is pretty large and made from 2 inch construction foam. 80inch span, 17inch chord, max section 2 inch (will have proper airfoil shape - TBD). Power will be via a 25cc weed eater engine. Having seen a similar aircraft in flight it's aerobatic but rather lazy about it (given it's size). It's not going to be overly fast.

Looking at my old 40 sized trainer I note the TE of the rudder and elevator are not overly tapered, in fact they end with a square edge probably 3-4mm (1/8th) thick. So if a trainer can deal with that I can't see how a relatively larger aircraft would be sensitive to 1/4 inch tail feathers with rounded edges.

However for the ailerons I intend to taper as much as possible.