Dedicated VPN router behind RT-AC88U- Why can't I access Asus webUI while VPN-ing in remotely?

Hello everybody, this is my first post here, so please be gentle!

I'm having issues with accessing my RT-AC88U web interface remotely via a PPTP tunnel. Basically, my setup is as follows:

-Asus RT-AC88U as my intenet facing router. (LAN subnet 172.16.0.0)
-Linksys LRT214 as a dedicated VPN server (LAN subnet 172.16.1.0)
-These two routers are connected by Asus LAN port --> Linksys WAN port (VPN won't work on LAN ports)
-The linksys gets it's WAN IP Address via DHCP (172.16.0.176)

I have a...

Dedicated VPN router behind RT-AC88U- Why can't I access Asus webUI while VPN-ing in remotely?