After adding up the left and right facing coins for each variety, I came to the following totals (just estimates as I may have accidently skipped a few entries):
In the Edith Schoenert-Geiss study of
Maroneia (Die Munzpragung von
Maroneia - 1987):
Right-facing: 24 and left-facing: 5 (82% right-facing)
In
Selene Psoma's study of the coins from the
Maroneia excavations and the Komotini Museum (The Coins from
Maroneia and the Classical City at Molyvoti - 2008):
Right-facing: 329 and left-facing 163 (67% right-facing)
Within this group, 133 coins are the 'Agathokleia'
types (there were more of this variety than I
had remembered) and they are all right-facing
horse foreparts. Subtracting the A-G-A coins, the remainder with the usual letters are almost evenly split between left-facing and right-facing horse-foreparts (55% right-facing).