Gentle tips with the horn will solve your problems my friend, tip slightly into the measure from your horn and back off, check it, tip a bit more, and when you get close, another careful attentive tip should do it. Practice filling your measure a couple evenings at home in your living room.
I Practice the same way i hunt,...no bench, everything you use to load comes from your bag and immediately goes back in it in the same exact place...
It won't take long to get a feel for tipping your horn and sprinkling a little at the end, to the point that you will be doing it with only a single glance for your final tip, as you keep your eyes mostly on your surroundings.
Funnels are nice, yes, but its an extra thing to juggle around when loading from your bag with the butt of the gun on your foot...
My philosophy is, why have more accoutrements to juggle around, carry, lose, or forget at home, when you can just have more skills and tricks for getting by with less...you'll never drop skills and tricks in the snow, leave them behind on a rock, and they won't bury your more essential acoutrements in your bag at exactly the time you need to take them out silently while keeping your eyes on a tiny spec shielded mostly by a wall of brush 40 yards away...