Tungsten size should be selected mainly according to amperage AND polarity and not always dependent upon metal thickness.
When TIG welding aluminum, If your tungsten begins to ball up and quiver, this means your tungsten is getting near its capacity. This can be minimized by using the A/C balance dial and setting it for more penetration and less cleaning…or if you are using a TIG inverter like a miller dynasty, the a/c balance should probably be set to 65-70% EN.
For transformer machines like the syncrowave, The a/c balance set to the cleaning side means more of the dcep side of the a/c wave which means more heat is on the tungsten tip = more wiggling.
The more to the penetration side, the more the arc is on the negative side and the Less heat on tungsten tip and less cleaning action but the square wave usually provides enough cleaning anyway even in max penetration mode.
A/C balance explanation Again… the Higher the number, less cleaning and more penetration and less heat on the tungsten.
This applies to square wave machines. So if you are using one of the older sine wave machines that have no adjustments for this, you might need to preheat material and use hotter gases like 50/50 argon/helium so that less amperage is required to do the same work.
If you weld a lot of thick aluminum...like 1/8" and thicker...get some 50/50 helium/argon.