Help with aluminum project

[Markz]

Ok guys...hoping I can garner some good advice here.
Recently received my PP256 for an aluminum project. I have adequate experience MIG welding carbon steel but have never held a TIG torch and never welded aluminum.
I'm able to run a decent bead on a single piece of 1/4" aluminum, nice width and healthy penetration but when I move to join two separate pieces the nice bead goes down the tubes.
Specs are as follows:

1/4" x 1-1/4" aluminum flat bar with mitered corners (as seen below)

225 Amps
CK 200 amp flex head, air cooled torch with superflex cable (figured I didn't need the handicap of learning with the bulky stock torch)
2% Thoriated 3/32 tungsten sharpened to a point and 1/4" stickout
3/32 4043 filler
#7 cup
100 Htz Frequency
30% AC Balance
100% Argon - 17Lpm
Pre Flow @ about 1 Sec
Post Flow @ about 6 Sec
No Pulse and no Slope

Thanks in advance for your help.