I've already posted this on the Microsoft TechNet forums, but his site seems to provide more informative answers, so here goes...
Here is my network configuration, in a nutshell.
Cisco small business switch is connected to wireless router (10.77.79.0/24) which is connected to the Internet.
Hyper-V host has two physical connections to the small business switch: one for management, and the other for the Hyper-V external virtual switch.
within Hyper-V there is an internal virtual switch which is hosting my server VMs (192.168.1.0/24).
there is a proxy server (a Hyper-V VM) which has two network interfaces, one connected to the external virtual switch (10.77.79.80; gateway points to wireless router) and the other connected to the internal virtual switch (192.168.1.1; no gateway). This proxy server has the Windows Server 2012 R2 RRAS role installed and is configured for NAT only. The internal VMs have a static IP address configured to point to the internal interface of the proxy server for both the gateway and primary DNS.
For the life of me I can't figure out how to configure RRAS on the proxy server to allow RDP connections from the wireless network. I've been searching for a couple days now with most posts saying simply "it just works"...it doesn't for me.
There are no firewalls in-between any device (software firewalls or otherwise). RDP works in-between the internal IP of the proxy server to/from the internal VMs, and vice-versa. My end-game is to RDP into the internal VMs from any device on my wireless network, providing the correct NAT and forwarding rules are in-place.
I'm hoping I'm missing something simple, or maybe my desired configuration isn't possible...not sure.