With Velox and other cloth tape I've had better luck going as narrow as possible while completely covering the spoke nipple holes. If there's a recessed channel, I get the tape that just fits in the channel without going too far over the shoulders.

When I tried wider cloth tape it interfered with seating the bead on most tires -- that goes for the 700x40 tires and wider rims on my hybrid, down to 700x23 tires on my road bike's 622x14 rims -- I think I used 11mm or 12mm cloth tape in those. Narrower tape solved that problem. No problems as long as I was careful to cover the spoke nipple holes.

The thicker cloth tape also fixed that problem with tubes extruding through thin rubber rim tape and splitting at the tips of the dimpled areas where the tube and rim strips extruded into the spoke nipple holes.