Wonder if you have to much airspeed over the short turn now, especially with the pushrod pinch opened up. I'd bet adding width to the short turn might help?
That would be my assumption.
The “test piece” is what I consider “SSR challenged”, so anything you do that might result in more volume trying to make it thru the port, makes any inadequacies of the SSR profile really show up.
However, I am curious to see what the long runner inlet adapter might do, particularly as the flow numbers go up.
I have had some “better” flowing sbm heads that had high lift flow issues(turbulence/regression) that responded well to extending the inlet opening…….. on only the floor.