Overhead welding with a 7018 can be done at the same amperage used for flat or horizontal, or close to it. Set the machine hot enough so that it won't stick when you hold a tight arc, and then... hold a tight arc.
16ga 6061 aluminum using 1/16" (1.6mm) 4043 filler.
I used a tapered 2% lanthanated 3/32" (2.4mm) tungsten.
Welding small aluminum coupons with a chill backing,
This can also be done without backing but on small pieces of aluminum heat can saturate the piece and the puddle gets very watery.