Ive tried this, you can only get a certain amount of water down any hose-pipe. Its irrelevant how many jets you have in the brush if you can’t feed them the water quickly enough.
There are lots of things that affect the water flow, hose diameter, pump output and pressure, weather, number of jets, controller setting your pump runs at, hot or cold, size of pump.
What Im happiest with is dependant on if Im using hot or cold, but with cold its pump at full bore, with 6mm hose and two fan jets on a 14” brush. If I could up the output I would but with this set up Im sure Im running at maximum with a 10litre/min 100psi pump.
I saw a 15LPM pump a week or two ago, can’t remember where, that would be worth a shot, but sure we’d be needing 8mm at least.