I suspect these guns with all the leaves folding are sighted and regulated to be shot at point blank range using only the 'rise of the breeches' to give the necessary elevation out to 25 yards or so - ie: point blank shooting as noted. This is how many muzzleloading for-India guns were sighted in the mid 1800's. No standing sigth was needed as the thickening of the breeches gave the necessary elevation to the bore rifles.