Joe,
I'd stick w/the published recipe; the Federal 209A is def a hotter primer than the older ones & I would not sub it for a Federal 209 unless you call Alliant first & they tell you its OK to do so. What primer is called for in the load data you are using?
I have also noticed in the published 3/4 oz. 20 ga. loads that Unique will leave some ash. Reducing the powder charge probably makes that worse, not better. Its not a big deal, you are going to clean the gun afterwards anyway, right?
If that is what's bothering you, switch to Green Dot. You will use less powder & not have the residue ash visible afterwards. Either way, stick to published tested loads & use a scale.