Before you solder the central pin into the tack, profile the skirt to fit the horn. Find a piece of pipe, PVC, a can, whatever, of close to the same diameter as the base of the horn and contact cement (or rubber cement) a piece of 220 grit abrasive paper to it. Notch your silver domes slightly across the centerline of the skirt with a large, half round file. Now sand the skirt to the correct radius on the abrasive paper to fit the horn. Solder in the center pins and drill a hole for each tack very slightly smaller than the tack pin. Apply glue (I use super glue) to the tack pin and very lightly tap the tack home making sure you line up the curvature of the tack dome with the surface of the horn.
You can also use a sanding drum with an appropriate diameter to sand the tack domes, but be prepared to chase them around the shop a lot and make a few spare preforms.
