Odd tire sizes and all time 4 wheel drive

2000 ford explorer. blew one tire on firrest roads and ruined the tire by running onit to long. remaining tires have /3 tread left. How important is it to get a replacement tire to match the circumfernce of the other three. I had three diffenert ford dealers with two totally differenet answers. two said no more that 1/4" diff. in circumference. ONe said " no worry that’s what the differential is for. I’ve got the spare on andit has never bee used. P235 75R15. old tires have 5-6 MM tread lect, the spare 13MM