Why, oh why, are we always told to wrap PTFE tape round the threads?? In a compression fitting using olives the waterproof seal has nothing to do with the threads. I put the olive on the pipe and tighten the fitting until the olive has gripped the pipe, crimping the pipe ever so slightly. Check that the olive isn't free to rotate on the pipe, but is gripping it firmly. Wrap three tight turns of tape round the olive in the direction of tightening the fitting. Do it so that each turn of the tape overlaps the olive on both sides. Do up the fitting, and Bob's your uncle.
As to forming a taper with PTFE tape on parallel threads, this is the common way of connecting a garden tap to its wall-mount elbow fitting. By trial and error, tape is wound onto the thread on the tap until, with the tap fitted and fully tightened, it's in an upright position.