When I was doing rust repair on my 73 charger, I experimented with two techniques which showed promise, maybe MP&C could chime in:

#1 For a patch with no access for planishing, I put an extra bit of crown in the patch. After shrinking, the crown pulls out, effectively preventing the patch from being distorted.

#2 where planishing is accessible, I would put a slight flange on the patch weld seam. During planishing, the flange gets hammered flat, effectively 'stretching' the patch, and compensating for the shrink.