I would not use a switching supply on the prescaler board.
I think at about 50mA, a DPACK or SOT-223 regulator should do the job and stay relatively cool..
Even the SOT-89 should be OK as the most of the heat will go to the ground plane through the tab.
And on that note, the tab should be embedded in the ground plane, no relief connection.
That is assuming that the tab is the ground pin on the regulator.
