I find a vertical..ish back roll harder for some reason..but if I do a quick transition, so take front hand off, grab back rail...vertical ish backroll then go the other way it seems to be easier. or try a double back roll transition (with a downloop), do the first one horizontally then flick over your head for the second one, dimitri does these well. Landed a few of these, but ate **** all the others....this season maybe.