As
@wimpanzee said, there is a limit on how low you can go. Unfortunately, that will vary by gun - mine runs great all the way down to 90 bar on the regulator without dumping the air (provided I stick with pellets and don't try slugs, as will dump with those at that level), and others have guns that won't operate correctly below about 120/130 bar. But even at ~90 bar I have no problem shooting JSB 18.1s at over 920 FPS, and I still get plenty of shots (well over 100 on a ~4300 psi fill.
I did find that the Huben regulator is less stable (has more creep) the lower you go with it. It seems happiest at around 140-150 bar. Since I wanted to run more consistently at the lower pressures, I eventually switched to a Huma regulator in it - I gave up the easy adjustability, but gained stability and a more consistent first shot speed.
I also agree that talking to Kelly is a great idea, but if you are even a little bit of a tinkerer then you won't leave it alone - the adjustability of the gun is just so much fun . . .