problem reaching parts of my network over wireguard vpn connection

[Alwin]

hello everybody :-)
i am new with opnsense, though not completely fresh with networks ...
but it seems i am too stupid here anyhow, so i ask for your kind help

i have a network 10.20.x.x with mask 255.255.0.0, and from a pc with the ip 10.20.7.94 i can reach all other nodes, e.g. 10.20.7.27 or 10.20.1.28 etc
setting up wireguard instance and one peer step by step following the opnsense documentation, i can connect via vpn and reach the firewall 10.20.7.27 and the pc 10.20.7.94 - but not the node 10.20.1.28 or any other node that are not in the 10.20.7.x range. of course i realize that there is a problem with masking somewhere, but i am unable to find it.

the LAN interface in OPNsense has the IPv4 address 10.20.7.27 / 16 , the WAN Interface is IPv4 with DHCP (connected to a Fritzbox with a fixed IP-address via DSL ) and with all searching i am unable to find a subnet mask problem or config that prevents the access to the whole network (10.20.x.x) and only let me reach the subnet, that has the opnsense firewall in it (10.20.7.x)

i very appreciate any help to solve this and point me to my fault in the configuration.