I don't have a keg so my statements may be way off base, I use the HM mainly on an akorn Kamado. That said, I have heard people talk about low startup max settings and creeping up the startup temp slowly and find that not to be the best method in my experience. Reason being, when the HM sees a slow rate of change in pit temp it will react slowly, when the HM sees a fast rate of change it will react faster. So when startup max is set high the rate of change is fast and the HM reacts faster to reduce the output as the temp rapidly approaches the setpoint.
I prefer to leave the startup max high (I use 100%), when I build the fire I make sure not to light too many coals (I use 1/2 a weber starter cube for low and slow). I let it burn with the lid open unit I see the smoke from the starter cube go away and then close the lid with the top vent open just a little bit. The pit temp should rise rapidly, the HM should react rapidly, the output will cut off on or before the target temp is achieved and the tight top vent will help choke the fire to the proper size. At this point the blower MAX value will kick it, I generally set this much lower (like 30%), so when the blower kicks on again it will be at a much slower speed. At this point I adjust the top vent so the HM runs in roughly in the 30% range to maintain the target temp.
This is just my method, I know there are many other methods being used since the HM setup is so flexible and the variety of grills it is being used on is so wide.