Last night I finally managed to get the strap length on the JAEbird sorted (I think).
I have been 'struggling' with it for a while. The DSL straps I have are brilliant once you have the length right, but getting there can be a pain in the arse, particularly if you have straplocks ... and loctite. The length is not continuously adjustable, so to change it, you need disassemble the strap and feed it through different slots (just fvck off with your 'ahems', I'm trying to be serious). All this is complicated by the JAEbird strap pins being above body centreline.
In the end, I took the Orville, fitted its strap and arranged it so the strap mid point formed the apex of a triangle, then measured from the E string to the apex. Then I did the same with the JAEbird, doubled the difference and added that to the strap length and damn me if they don'l feel pretty much identical now.
So there you go boys and girls, the secret to setting a perfect strap length is maths.