Yeah, I was thinking I might want a tighter bend but I've not worked out dimensions yet.

Hows about using a couple of elbows in the pole. The vango helium use them rather than a continuous hoop and with a carbon fibre pole its very stiff and possibly gives you a bit more space.

Obviously a longer pole requires less pre-curving as each mm / inch / foot has to bend less for a given radius. If you look at poles for most hooped bivvys the sections will have a bend in. With alloy, it's not hard to do at home as long as you're gentle / careful.