That shows exactly what I keep trying to tune. The flat mid range that takes a big jump when the power valve opens. On my 2011 using a NEDW needle and adjusting the power valve linkage so no free play I had good success. On my 2005 I'm still chasing it and have not been successful with jetting and power valve linkage adjustment.
Thanks for posting and look forward to hearing the results after a head mod. I had RB do my head on my 250 Beta and it really helped the midrange before the power valve opened.