I have a short LP too so did some research on it. TB has some folks who were successful at 8/9 days (some without any treatment) but nothing shorter.
This last month I peaked (CBFM) on CD 22. I've never prayed for my normal 28 day period to be late like I did this month. (I knew I wasn't pregnant as we took the month off.) DH was so confused as to why I was excited every day AF didn't come but wasn't rushing to take a test. (AF finally came on day 32, so FX it will stay in the 9/10 day range for us instead of dropping back down.)