I can't leave them permanently coupled because the plasma cutter needs to be protected against sawdust and other stuff that could get inside it from the shop's interior air. So, the plasma cutter gets "put away" when not is actual use. Also, I figured out that I COULD get by with a LITTLE less than 25 feet, but my choices in 2 different sroes came down to 5', 25', or 50'.In your case of trying to maximize bottle usage & as much pressure retention throughout the bottle life that you can , I would shorten that air line with the quick coupler to the absolute minimum you need ( position your plasma cutter as close as you can. The optimum thing would be to do away with that quick coupler and join them solid....every time you disconnect there is going to be an escape of gas equivalent to that long hose ID...that PSSSHt you hear every time you uncouple in this case is money not just air.
The entire cubic volume of that 25' long x 3/8" diameter air hose calculates out to about 0.02 of a cubic foot, believe it or not, so it is actually very small. I was astonished at how small when I did the math (twice to make sure I did not make an error),