Ok... this is what I tried.
Think corner or t, although the re-world isn't exactly either.
Power and wire speed to match thinner metal. Beaughtiful lookiing weld, but failed hammer test. Flowed into thinner material but hardly bumped the surface of the thicker material. Tore loose on only a couple hammer blows.
Compromise between power and speed of thicker and thinner metal. Crappy looking welds all the way around.
Power to match thicker metal. Keep spray stream aimed at thicker metal with quick stiches into thinner metal. Not pretty welds, but not ugly. (well not all ugly) Good penetration. Odd appearance of thin lines of extra metal or spatter off the edge of the bead on the thick metal side. Will grind and see what it really looks like . Occassional blow through on the thinner stuff. Mostly near ends or when my glove caught on something and I didn't let go of the trigger. I was able to fill the blow through spots by dropping the power by half, and running the wire as fast as it would go without stabbing. Those fills are purely cosmetic I am sure.
I have a couple more welds to do where I will be welding 3/8 to 1/8 for 24" beads. What should I try to improve my appearance, and keep my weld quality or do I just need to keep doing the saem thing, and practice more?
This is all 5052 with 5356 wire.
P.S. 3/8 to 3/8 aluminum is pushing the maximum limit of this machine. I have to slow stitch to get a decent weld, and it is not pretty. Now I can say I have pushed both the upper and lower limits of this machine.