Display's native resolution not registering properly
Tried doing an SMC reset, followed by a PRAM reset; neither worked.  Tried switching ports on the mini using an HDMI-Mini DVI dongle and starting up as the only connected monitor on this new setup; no change.

In the end what did work was switching to the monitor's DVI port and using a DVI-HDMI cable that came with a new monitor I'd picked up recently.  Screen now registers at the appropriate size and without scaling.