First you still need to take the powder measure appart and inspect/ clean /tighten. You appear to be fighting doing this. Not sure why. Its not that hard.
Next I have loaded lots of promo in the past. Your on the edge of where it will meter consistently. The Xsmall bar make things worse. Standard pisto bar would meter +/- .1gr. Xsmall would be .3+/-. 3.5 seamed to be the "brake" point. The more you go below that . The more inconsistent. The more above it became more consistent. As you stated Promo is a large "flake' powder. It needs a large hole to fall into.