well, its mechanical, no amount of tuning can change that
however, being a valve that uses the pressure difference of the throttle body to open/close, thats why i put it down to ECUs.
at lower RPM you have throttle limits, andys may limit it differently. his may slam the throttle shut when he backs off, or maybe its more gentle.
andy put your stock ECU back in and go for a drive. see if it does the same thing