Thanks for posting your article. It's very informative and helpful. I have an MS Access database of every unit in the army as of August 1914 and it lists as you mention in your article, 1 Bavarian and 4 Prussian battalions. It's apparent that these units expanded as the war went on. 7th Battalion is obviously one of these.
I'm assuming that FEA 7 was a Prussian unit and therefore the Prussian button is appropriate. Do you know if that's a fair assumption?