I've seen a nice leather quiver before and really its design wasn't that different from a side quiver but rather attaching to a belt would clip to the upright of the leg support. Though admittedly this was for a gentlmen with only one leg so in fairness had a bit of space to allow a quiver there.
I'm not sure how well a quiver that also belted to the thigh would work. True it would be steadier when standing still but when moving wouldn't it be still moving rather than left to right when arrows would be moving back and forth.
As for the back quivers I like the designs, though I agree the bottle holder on the front of the back quiver won't be easy to get at. The first design though looking nice I presume the original section is the only part the arrows go in, the other sections would just be for looking nice.
May I ask who is your quiver design aimed for, in the sense is it for a target archer, field archer, hunting archer, LARPer? I'm asking because each has different needs from their quiver.
-A target archer can be more bulky as really its just a place to store arrows but also protect their arrows and keep them straight,
-A field archer (I'm guessing) will want something more streamline and figure hugging, and arrows won't want to poke above the shoulder too much so as not to catch whilst walking through the forest and allow them to bend more without arrows falling out.
-LARPer will be wanting something to look nice, easily draw from.
-Hunter (again I'm guessing) would want something to allow them to move through denser undergrowth and perhaps draw with minimal movement to not spook the animal.