Is slipping for me - NcSTAR AR Handguard Removal Tool

I have this four stars since it after 15 to 20 uses (including quite a few "slips"), the rubber coating is still intact. The coating appears to be applied properly. I took away a star since i'm unable to get this tool to stay in place when it is hooked around the front edge of the lower receiver (LR) magazine slot. When i apply a clamping force to the ends of the tool and push down, the hook comes off the LR. Anyway, maybe i'm doing something wrong, but i am a trained armourer. I'll keep practicing.