The VPN settings in quickset isn't really "site to site". It is rather typical road-warrior setup and there is no need for same subnet - your devices will be able to communicate with each other so why limit yourself by putting everything on the same subnet? If they are not able to communicate, then you got just a simple firewalling mistake which can be fixed.
If you really need to have them on the same subject, keep in mind it won't be direct L2 connection so your router will still have to behave as a proxy. There will be multiple changes, not just the "local address" in ppp profile. You will have to add arp-proxy on the LAN interface (probably your bridge), you will need to change IP->pool for the vpn...
it is hard (rather impossible) to give better info without having full config (you can export it with command
/export hide-sensitive file=whateverFileName
If you ever want to set up a VPN between multiple sites on the same subnet: Not possible straight away - router has no chance to understand whether you want to communicate with IP from your site or from the other. Similarly, your PC have connected route with the local subnet, so it won't even bother to contact the router. You can overcome this partially with arp-proxy, but then IP colissions will appear. (because each site can have the same IP active unless you make sure they are all different by manually setting them or by giving different pool to each DHCP)
It is possible with some creative hacking and NATting (to make those subnets look different) but I would not recommend that at all. It would be a nightmare.