Hi Sluglife, could you please post an image of your “drop clips” rigged. They sound like they would help me diving off my boat. I use the loop of cord method with a double-ender but find it a bit tricky to manage due to its proximity to the New Zealand ROC (Ring of Confidence for Hydro/Visual date) plastic loop around the tank valve. A tied on bolt snap does sound easier…
It's not the best picture, but you can see it on the blue-tank near the valve. The paracord starts at that small 1-inch d-ring, and goes to the large bolt-snap.
My loop I think is 6-8 inches when stretched straight. However, there are a lot of variables here, such as my height (I'm about 5ft 11in), where the cord starts, tank-height, bolt-snap length, chest-d-ring position, etc. What you'll want to do is start out with about a 7-inch loop, and then see how that works. You want it long enough to provide adequate flexibility when donning gear, but short enough that when you stand up straight, the bottoms of the tanks are lifted off the ground by at least a few inches. The idea is to be able to clear small obstacles and take a giant stride.
As a "DIY pro tip" on not wasting paracord, start out with about 20inches of paracord, and tie the 7-inch loop, and don't trim the ends. See how that works, and then tie/untie it longer or shorter as needed. Only trim and burn the ends of the paracord once you have a length you like. (I find I more frequently waste more material, by starting out too-short, than too long).
As far as that plastic ring, this "drop loop" doesn't have to be "tied" anywhere specific. For example, I could even secure one end around the valve-neck, and the other on the bolt-snap, although the paracord might want to tangle with the regulator.