“Sefer Ba’al Hama’or” sounds redundant and awkward, no?
Originally Rabeinu Zerachiah Halevi of Provence’s corpus was called “Sefer Hamaor”(and one could call him “Ba’al Sefer Hama’or”), but with time the author was called simply the “Ba’al Hamaor”. It was further delineated by the “Maor Hakatan” on Brachos and Moed, and “Hamaor Hagadol” on Nashim and N’zikin.