So coiling doesn't change the end length of the cable? 3 ft regular is the same length as 3 feet coiled?
No, it doesn't work that way unfortunately.
When I say "6ft", it's the length of the raw cable that gets cut. Adding a coil will shorten the cable. To figure out your desired cable length, multiply your desired coil length by 6, and you'll solve for the length in inches required for said coil.
ie: 8" coil uses up ~48" of cable. Effective "loss" in length is 40". Hope that clears things up.
For reference, a 1ft coil requires 6ft of cable.