There are several attributes at play for either max gross wt (flight) or max landing wt. For the most part, the max landing wt is for the gear and attach points along with an associated VSI----which I am not sure what was used.
For flight, the things under consideration for max gross are:
-load factor----the aircraft was designed with a certain G envelope---and that was developed using max gross wt. If you go above the published max gross weight, you need to reduce the G.
-Takeoff/landing length
-braking capacity (higher gross wt and higher landing speed=more kinetic energy to dissipate)
-climb rate (if you get too heavy, you finally get to a climb rate that is unsatisfactory)
-offroad emergency landing (the higher the gross wt in a canard, the more it is going to hurt when you land----the nose gear and sometimes the main gear likes to shear off----when the main gear does not shear, the nose likes to dig in and swap----the higher the GW, the more dramatic the effect)
Adding a more powerful engine and good brakes can help alleviate many of the performance issues----but won't help with the G load or emergency landing
There are several ways to fill the gap----I even saw a new way within the last week or two---now can't remember where. But you can use silicone or glider tape to fill. If you silicone, one technique is to tape both sides of the gap. Then smear in the silicone with your finger---make it look real nice, then pull off the tape before it drys. When you take the wing off, you will need to slice into the silicone with a razor blade.
