Water is about 30x more dense than air. So every fin kick is trying to push a LOT of mass with a lot of drag through the water. Less drag equal less air trying to kick your way through it. So the "fuel consmption" is the air in your tank!
Where things go wrong is people begin to eliminate things that have nearly no bearing on drag. As in air, a sphere, or cylindrical shape presenting it's side to the wind or water, presents VERY little drag. Eliminating a LP hose will not cause a perceptible difference in drag. When you look at a diver moving through the water, the shoulders and head are breaking the plane of the water in front of the diver. This is why technical divers place pockets on their thighs. That plane of water has already been broken by the shoulders. They are in the slipstream.
What causes a LOT of drag is tanks. This is why going to 2 tanks won't give you twice the time. The extra drag induced is high. This is one reason I don't like tank mounted pony bottles (among many). You incur the drag of adding a second tank, but since you don't breathe it, you gain none of the benefit in terms of air consumption. Better to use double tanks and get some breathing gas for all that extra drag, or put the pony behind the shoulder and keep it from adding so much drag.