The more you can stabilize a MEC loader on a sturdy bench/table the better. Operating the handle sequences in a smooth fashion the same way every time will also help with consistent powder drops.
I make sure the bar/head fits snug on the mounting bracket in the back of my MEC loaders to prevent bottles from shaking back and forth and use the rubber/brass inserts from MEC. Replace the worn out brass and rubber inserts to prevent powder migration. Some bottles also need a tad of trimming in the openings to prevent over tightening also. A lot of reloaders fail to do that part and find a bottle too tight will bind the bars travel back and forth!! We know what that leads to?
Some have figured this out and that's why we see some say it makes no difference and others saying it makes all the differences??