It sounds like you might be applying too much heat. What fan speed setting are you using? At that distance I certainly wouldnt go higher than the second setting.
You might want to consider a mount for your HG so you can keep one hand free to adjust the controls. Also consider a larger bowl which doesnt concentrate the heat as much from your high-powered HG.
I have the same HG on my corretto, I start at around 540 with fan setting 2. I dont wait until the HG reaches that temp before hitting the beans. The HG nozzle is about 25 cm above the bean mass (depth of the BM breadpan).
My temp is measured by the DMM, not the digital readout from the HG Im still trying profiles at present but it goes something like:
540 on the HG for the first 5mins at fan speed 2
Bump up the fan speed to 3 then adjust the HG temp control to maintain a heat ramp of about 10 degrees per min (it typically increases to 580 - 600 depending on ambient conditions.
At RFC, drop back the HG temp to about 560 - 570 to get a heat rise of 3 - 4 degrees per min to coast to SC or beginning of RSC
and I would have much different thermodynamics to you.
Hunt around for a 2nd hand BM to do the agitating Jon.