I always put a flow control valve on and just give the motor what it needs. The excess goes back thru the case drain fitting. The return line does what it’s supposed to.  These new machines build more flow on standard flow than the old high flow used to and on cats there is to much flow for small motors to run continuously.  The excess flow is released in the internal hydro system and very soon wrecks the bypass valve spring since it gets very hot. Went thru a lot of machines till we figured it out.  It sounds like you did something like this already so I’m prob not much help and I’m not familiar with set up you are using but if it works I want one .