Supermoto,
Every welder welds slightly differently so just take the advice you have been given and try it out. It is quite possible you will end up doing something completely different but if you use the advice given it is a starting point.
I have never done GTAW on plate but I have welded thousands of GTAW root runs on pipe and the problems you are experiencing on 4G plate are the same as the bottom of a pipe, shovel the wire as fast as you possibly can. Gravity is working against you instead of for you as you mentioned.
2G is not quite the same but if you are not getting enough pen but you are picking up the edges, don't change your amps / volts / travel speed, just try feeding your wire a bit quicker.
Hope that helps,
Cheers,
Shane