I got my servos from BST too so likely the same, I think the thing with the drive number setting the drive up is that it has no idea what load the motor has - its just a ballpark setting. The downside is the manual is written Chinglish and unless you know exactly what parameter does what, then its all guesswork.

I spent hours and hours tuning, its made harder as you also need to test each tune at multiple speeds, I test at 3, 13,23,33,43 and so on as % of full speed - its easy to tune so that it runs great at say 60-100% but oscillates badly below 50%

In the end i tweaked in the order P - D - I until the following error was as low as possible, then added some kVff if needed.

I'm still not happy with it though but at least the mill is running now. No doubt an expert could tune it in minutes but I don't know any mobile servo experts ;)