I believe they make different lengths. I am LH as well and I use their 25 MOA rail on my Annie. I have about 15 mils of travel on my scope plus the 7 on the rail for 22 mil total. That gets me comfortably out to 400 yards. I also have 10 mils on the windshield which gets me to 500 yards (Never tried that).
How far are you shooting?