If you mix the spice with the milk before you add it to the other stuff, it should work a bit better to avoid the pockets of flavor. You’ll still want to stir the finished product, but as long as you don't give it time to separate before pouring in, should help a lot.

You can also make whatever kind of microwave popcorn you want, just get some brown paper lunch bags and loose popping corn, put about a cup of corns in the bag, fold the end over several times, and pop it like regular microwave popcorn (you’ll wanna watch the time until you get a feel for how long it takes, since the volume is different than pre-packaged) then take your seasoning of choice and either sprinkle on directly (if powder seasoning it should stick fine without help) or spray some water/drizzle some butter or oil and use that to stick on your flavors if they are bigger bits. Im a big fan of garlic and sweet onion popcorn :) and if you skip the oil, super healthy snack. I kept a jar of corns and a small spice cabinet at work so I could make it whenever, was lovely.