Actually, swing axle has a short line by the torsion bar and is solid the rest of the way, just like IRS. But, on a swing, the flex is from the frame horn to the axle. Not sure what you mean, Gordon.
FWIW, I have braided SS/Teflon front and rear. On my 4 wheel disc I use stock length flex lines in the front, but longer ones in the rear from the firewall al the way to the caliper. My pedal is solid as heck. Yes, even with repeated heavy application, as in actual track time. No fade in 30 minute sessions.