The risky leap from big screen to small has apparently paid off for Geena Davis , 44, and Bette Midler, 54, for now at least. The debut this week of their two respective sitcoms, ABC’s “The Geena Davis Show” and CBS’s “Bette,” have delivered high ratings, especially in the case of Davis. On Tuesday, her domestic comedy averaged 17.3 million viewers (a 7.7 rating/19 share in the key adult 18-49 demo), according to Nielsen Media Research. And this was despite some of the worst reviews to greet any new show this season. Meanwhile, Wednesday’s Bette Midler vehicle, in which the star plays a madcap show biz diva named Bette (no last name is uttered on the show), averaged 15.72 million viewers and a 5.5 rating, topping its competition on ABC, “Who Wants to Be a Millionaire,” in the key demographic group of people aged 18-49 (5.5/16 vs. 4.2/12). If these numbers keep up, say TV observers, Davis and Midler can look forward to long runs.