I've used auxillary shielding with automated MIG equipped through a TIG fuel lens setup with the electrode hole plugged with a screw. You have a good weld, and additional shielding will address the problem, so you could prove this with an experiment, then figure out if feasible to work with https://www.madanijayateknik.com/service/detail/as-round-bar-plate-sheet-stainless-steel-409-409l-409m-409cb-409ti