The lines to look for are in the [ pit_lane_0 ] part of the ini.
begin_stall_entry_offset = 18.0
begin_stall_approach_offset = 40.0
(taken from the Noonan conversion of Myrtle)
The numbers are distance before the pit stall in meters and with how the tracks are built meters in curved parts aren't quite the same as in straight parts so it's about finding a happy medium where the cars pitting in a curved part doesn't moonwalk and the cars pitting on the straights doesn't run through other cars pitstalls. Don't go too crazy to begin with, increase both (although I think entry offset plays a bigger role) with something like 2 meters and see what it does.
Another line you could play with is
slow_pit_line_dlat_offset = 0.0
Setting it to 1.0 makes the cars move 1 meter closer to the pitstalls before pitting so it could help them find their stall in time and not get dragged in. This depends on how wide the pit road is, if it's narrow it's better to keep it at 0.
After that it's trial and error and some foul words