I get the same gap on my SE5a. The reason for the gap, in my opinion, has to do with two things.
First the full size plane uses fasteners on the front and rear spars to connect the wings to the center section. Second has to do with the stagger of the two wings. The top wing stagger adds weight to the forward section of the upper wing. Consequently there is a natural seperation from the back part of the wing. You dont see this on the full scale due to the wing attachment method. Just my 2 cents.