Shooting full loads
Shooting full loads is OK, and much preferable to leaving a gap between the powder and the ball. Full loads are rarely as accurate as slightly reduced loads, although each gun is different and some may actually do better on full loads.
You do not need to fill the gap between the ball and the cylinder face with grease - it is sufficient to use just enough to cover the opening (the theory is to provide a "seal" to prevent sparks from entering from the front and igniting the powder). Back off on the amount of grease.
Regarding seating the ball. You are right to push it down onto the powder charge, even though that leaves a considerable distance to the cylinder face. The idea is to 1) compress the charge to get consistent burning, and 2) remove any gap to prevent a pressure spike.
In my experience, there are two reasonable solutions to the dilemma of the ball not fully seating with the loading lever. I either use a cornmeal filler between the powder and the ball (measured by volume, of course, to make up the difference between a full charge and the load you are using) or a lubed felt wad cut to the cylinder bore. When using the felt wad I do not use any grease sealer over the ball.
Using a full charge is certainly a third acceptable option, but then all my guns shoot better with reduced loads; I only use a full load when showing off (big bang, smoke, flames, etc.)