How do I make the overlay/HUD smaller?

[FBX Recorder]

Go to the Overlay tab in the main app window. You'll find options there to turn off what's displayed in the Overlay, so you can reduce it to a single 'X' icon.

Or have it display the FPS, recording duration, webcam and mic recording status, the 'stop recording' shortcut. Whichever way you want to go...