Hey, you're a good hand on electrical stuff I bet you ALREADY know this. Sure, as you increase the load on a motor the amperage increases and likewise if you're welding at low amperage she's not pulling as many amps on the welders input.
Without looking back at his post or in general the Full Load Amps (FLA) as best I recall, lol its been a while remember, is the number I used when I designed a motor branch circuit. If I designed for FULL LOAD figures, that should have taken care of it I figure.
Have a Happy Thanksgiving George