Rear camber issues

[Numplumb]

My rear upper wishbones are a lot shorter than the lower ones.
MX5 rear upper wishbones are a lot shorter than the lower ones.
As far as I know unequal length wishbones are the preferred arrangement.
IMO making longer adjusters or moving the anchor points won't alter the geometry enough to be a problem, there isn't very much movement in the rear suspension anyway, and if you set it at 1% negative at the ride height it probably will only go to 0% when cornering.

Regards Mick.