Assuming that you're asking me about the spread between shift point and recovery? I'm not a converter expert by any means but based on what I see on the cars I tune the mfgs have been narrowing the RPM drop down to something in the 500 to 600 rpm range. The explanation is that they are trying to keep the engine near peak power all the way down the track. In the old days the rule of thumb was to drop the RPM from power peak back to torque peak but now it seems to be to loosen up the converter so the RPM stays almost flat going down the track. I've seen some data logs where the engine RPM is very flat. That is typically with a glide rather than a three speed.

I don't know the answer on this car which is why I suggested he talk to a converter mfg. I'm pretty sure they'll tell him that looser will be faster.