I wonder what the optimal posture be for these dragons when flying/gliding?
No, seriously. I'm just not seeing any practical way those forelimbs can be tucked away against those (necessarily) massive flight muscles... which leaves pointing them forward, a la Superman. This could work in conjunction with the long neck, the basic idea being that you want your dragon to look something like a jet airliner; a narrow, streamlined bit sticking out in front looking a little like a torpedo, wings toward the back, and another narrow, streamlined section after that.
For this reason, you'll want your dragon's forelegs to be able to rotate at least 90Â°, so they can tuck those paws in along their necks.
This also gives you an excellent excuse to add large, backward-facing "ear" membranes to your dragon; they tuck their forepaws in behind these to minimize drag.
Alternatively, maybe they can dislocate their shoulders in order to tuck their forelegs to their sides, sort of like how the arms are on a human as opposed to a quadruped.