Yes - I'm cutting the center section, leaving the side walls to protect against pebbles, water and falling clothing

NO!
while im certainty very opinionated, there are few mods that I will outright say NO to. by cutting the sides off the belt covers you make it easy for debris to get in, but hard to get out. ever drop a guitar pick in an acoustic guitar? same principal.
ive pulled TABLESPOONS of gravel out of similarly modded belt covers.