I've done some research and OpenWRT (which Gargoyle uses) employs dnsmasq as a DHCP server.
This server assigns IP leases using a hash of the MAC address. There is a way to change this to be sequential. The way to change it is detailed here: https://forum.openwrt.org/viewtopic.php?id=50684.
Unfortunately, I don't know what I'm doing and I can't enable it Could somebody help me out?