pfSense

Tunnel Network description says:
This is the virtual network used for private communications between this client and the server expressed using CIDR (eg. 10.0.8.0/24). The first network address is assumed to be the server address and the second network address will be assigned to the client virtual interface.

Apologies if I am reading the above incorrectly however looks like the first address is actually assigned to the ovpn client (not the server/pfsense).

For example
Tunnel network = 10.10.10.9/30
assigns 10.10.10.9 to the client

client log:
add dev tun0 local 10.10.10.9 peer 10.10.10.10