Re: Mainsheet Cleat: on traveler or fixed?
Our entire mainsheet tackle moves along the traveller, it's not an issue, but ours is on the bridge deck, not at the back of the cockpit.
If by 'vang' tackle you're simply talking about a self contained multipart with a cleated fiddle block, that's a pretty standard mainsheet arrangement.
I think your current setup might be improved by moving the aft center mounted cleat/block forward of the helmsman's position,(ie run it along the boom and down forward) esp if the boat is tiller steered.. it's a more natural reach, one hand on tiller, the other for the sheet with no reaching/twisting around to keep it to hand..
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)