Hi there,
Ok he is my take on this issue.
Firstly you must have a flow control valve fitted to your pole - preferably the "thumbturn type" - next make sure your flow controller is on at least setting 8 imo.
Then when you clean a window you can first open up your water flow fully and do the frames and wet the glass. Then you can close your water flow up for a quick scrub if needed - i find if you leave the water flow on you do not get enough friction with the brush sometime to scrub away harder deposits bird muck etc.
Then you can open flow fully up again for the rinse - which is better and quicker as you have your varistream set high.