I'm right handed and wear my shooting pouch and horn on the left, high enough to clamp under my elbow when moving quickly. I have a much easier time filling my measure without spilling as well.
I too, worry about sparks when I see someone, especially a flinter carrying his horn on the same side he shoots from. I think Range Safety Officers, or anyone for that matter who sees a shooter shooting while his horn is unplugged should say something to the shooter. Same-o same-o loading directly from the horn.
Three Hawks