I've always wondered about Henry Anthonison - the name sounds like it has French origins - interestingly, John Harman apprenticed with him as well, if I recall correctly.
All the other observations - the slim lines etc - this is the way a Georgian period fowler should be - everything tapers from the area right behind the cock - forward and back, and everything is visually balanced. Simple sophistication in the architecture and decoration.
The muzzle bore is often greater than the barrel OD at the waist. You see really no wood on the forend when viewed from above - the stock and barrel form almost a figure 8 in cross section. No true large flat surfaces anywhere to break up the flow.
From what I've read and seen, don't assume the military officer's pieces were always bulkier. The military pieces made as officer's fusils were often made along the same lines as the sporting guns by the finest shops, but often had the wood cut back at the muzzle and a lug fitted for a bayonet. In England at the time amongst the better off, first born son inherited the land and title, second son often received a purchased commission in the military, third often went to the clergy. After the warrant (I think it was in the 1740s) officers were supposed to provide their own firearms, built to certain general guidelines, but still a lot of latitude, in lieu of the earlier halberd. So the best London makers made up sporting guns and officer's fusils along the same patterns.
Guy