Since you are in PyFerret, you can change to a system font and set the font size with something like:
SET TEXT /FONT=carlito /ISIZE=0
(where ISIZE is -4 through 4)
Another option in PyFerret is
SET WIN /TEXTPROM=1.0
that actually scales all text drawn in that window.
(PyFerret implementation of /TEXTPROM is quite different from that of Ferret.)
Hopefully some of this will help you get what you want. Using PPL commands in PyFerret for text bypasses the usual scaling and adjustments for text in PyFerret.
Karl