Welding Tips and Tricks

Hello, my name is Carlos. I work for a company specialized in Aerospace fluid systems. Basicly we bend and weld (manual TIG) stainless steel, aluminium and titanium tubes. We are currently having problems welding aluminium because of overlap defect. We have to weld properly 6061T4 0.5'' diameter and 0.035'' thickness tube to tube samples in order to get a certification for a new client. The parameters we are using are: 0.8 or 1 mm diameter 4043 filler rod, 22A or 25A, 1mm or 1.6mm (edge shaped) pure tungsten electrode, 60Hz frecuency, balance 23%, 8 or 10 liters/min argon shielding gas, mechanical cleaning before welding to avoid porosity. We have made some samples without overlap defect but we arent able to get continuity. I would like to know if we are missing any important parameter or which ones are the main tricks to avoid overlap defect. I'm conviced we tend to add too filler rod making the welding bead to spill over the not melted base material. However, if we dont ensure the penetration we can have a lack of fusion defect. I will really apprecite whatever advice.
Thanks a lot

Only thing I can say is lanthanated tungsten if its an inverter machine. The rest is beyond me sorry.