Tunnel IP address assignment mismatch

My regular node default tunnel assignment IP addresses start with
172.31.86.180. Yet when I assign a tunnel, it gets/gives/stores a
172.31.87.x assignment!

Why?

Each tunnel assignments appears to use 2 IP addresses.
I see an even number, my neighbor client nodes seems to use the next higher (odd) number.
May I use a 44./26 assignment to cover the 56 possible addresses used
in the maximum of 28 tunnels?

73, Chuck