The only settings that are user definable are the SSID, which is set at Settings > General > About > Name, and password, which is set at Settings > Personal Hotspot > Wi-Fi Password.
Address range is not modifiable.
Just checked my hotspot, and it matches what other users describe:
The iPhone has a small DHCP address pool that can give out 16 addresses (172.20.10.0-172.20.10.15). Of these 16 addresses are 3 taken by the network, broadcast (172.20.10.0 and 172.20.10.15) and iPhone itself (172.20.10.1). Leaving 13 addresses for other devices.
Your defined range seems unusual.
Maybe it conflicts with your carrier address scope?
Some results from searching on the net: 1, 2 (too lousy to be called "References". It appears you cannot set the range on Android either).