Hi Bill,
How far is your sensor away from the flattener at the moment? It does look like it is a few mm off the optimal spacing.
As for the images showing distortions when the sensor is too close and too far, curiously I found last night that when I moved my sensor further away from the 0.75 Riccardi reducer, stars in the corners got worse and looked more like in your image - a 'Star Trek warp speed' type, and when I moved the sensor closer to the reducer, star shapes improved. So I'm not quite sure whether the images showing different distortions when too close/too far apply to all reducers/flatteners
It would be best to add a small spacer and see if star shapes get better or worse, so then you will know which way to go.