hEX hotspot with open wifi ~ VPN can't open web gui of wifi inside

The hEX box is setup to be a Hotspot, so the initial wifi router (ether2) internally is open and working.
On that Wifi the WAN port is connected/merged to the LAN, and the WAN is disabled (as well as DHCP) on the internal open wireless router. (It’s just an old tester D-Link with dd-wrt, in router mode.)

I established also a VPN via PPTP connection, ultimately so I can access (amongst other servers etc.) the WIfi routers Web GUIs from a remote location.

I can access the web GUI interface of the Open Wireless router from the internal machine both plugged into it directly or through the hEX box since the Wireless router is basically a switch, (totally open and doing no NAT, nor DHCP, or even WAN, etc.).
When I’ve established the VPN from outside the hEX box (connected through another router to the internet above that), I can ping and access the network file share both ways with the appropriate IPs, but I can not (for days now) figure out how to access the WIFI/Wireless routers GUI from the VPN even though it’s accessible from the internal machine.

When I add an IP>Address with it’s statically set IP, I can then finally ping it, but when I open the GUI through the web browser of the VPN (external) machine it gives me the MikroTik hEX box GUI with WebFig login V 6.35, and not the WIFI’s Web GUI access interface.

I have tried a lot of possibilities basically too numerous to exhaustively list here.

If someone could shed some light on what is happening and needed to route the VPNs web GUI request to the correct device I would be grateful.

I was trying to integrate hotspotsystem’s MikroTik config.
It seems incompatible with those goals.
I started from scratch and got things working, alas with one last issue or bug on their end.
Still there might have been a way. Ultimately this is too specific of a problem to worry anyone here about anymore.
The time I’ve wasted would probable been better spent taking the longer route here.
http://wiki.mikrotik.com/wiki/User_Manager/User_payments