Re your backstay... replacing that piece of line with a multipart tackle (6:1 min) will probably get you where you need to be. If you're worried about the security of the adjustable part, then have a wire piece made up that loosely competes the current backstay, and connect it to the deck and the split part. It will slacken as you tension the backstay adjuster, but provide a safety in the unlikely event that the adjusting tackle were to part.
Our boat is a similar frac rig to yours, with perhaps more severely swept spreaders. I've just replaced the shrouds and headstay with new wire, but have gone to an all-spectra backstay system, and a cascading 12:1 on the same split arrangement that you have.
And I agree with you (and the others) that you should be getting the reef tack down to the normal gooseneck position. Close the slot as heinzir suggests, or learn to live with letting out a couple of slides.
I think you're doing great here, btw!
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)