Some flies can work with HP outputs some can't just the luck of the draw, what I can tell you is that if it has the standard ASA fitted to the grip, the Myth wont fit.
There is not enough clearance for the gauge of the reg when you screw your bottle in, it will foul on the rear of the grip frame, you can of course move the ASA back but it practically is hang off the back by the time it's in the right position.
Simple answer then, get a Ninja reg, take a few shims out to run on LP, also it'll fit first time on the ASA