i know exactly what you are going through. im having the same problem. im using a sigelei zmax v3 and i feel when i screw the protank on it has a terrible air flow. so what i do now is not tighten it all of the way. it works perfect now.
I hate how tight the draw is on the Protank, everything else about it is fine, it's just the tight draw that's a problem. Is it possible to make it draw like a un-modified RBA? I'd love to keep the tank but if I can't fix the draw it'll be for sale for sure.