Exhaust valve or cam reversion

My FormulaS has a 232* cam, idles at 700, fairly smooth, and does not do what yours does. I used to leak mine down every once in a while. It was always 4% or less.With new file-fits it was close to zero LD

Bad ig timing can cause misfires,which in a small pipe can suck the paper in. So can sticking or burnt exhaust valves. Reversion has nothing to do with that. Reversion happens on the intake side. The reverse pulse in the exhaust is a function of the header.Thats kinda how it works. It really shouldnt make it all the way out the tailpipe.
The misfire can be interpreted as normal on a big cam engine. 230*@050 is not big. When correctly tuned, it should idle at 750,almost dead smooth, at around 11/12 inches.
Yours, Idling at 14plus inches: either the ignition timing is over-advanced, or the idle speed is too high,or the cam is not a 230*,or the gauge is bad, or some combination. In any case the tune may not be there yet.
10/11% leakdown in my book is inspection time. You didnt say where the pressure was going. Hopefully its exhaust valves, cause that would explain it.
Theres also a good chance that the valves are just carbon fouled,so before you tear it apart,do a plug-check and adjust the A/F accordingly. Then put some top-end carbon cleaner through it, and take it down the highway and clean her out. Then redo the leakdown and see where thats at. At 11% LD youre giving away a lot of performance.
Good luck