Right, but my point (poorly worded) was that, if you have the strength to keep your legs elevated (utilizing your core), it puts more strain on your arms and back to do the pulling. So, hypothetically, lets say your in some kind of harness or sling that keeps your body in that L position (bent at the waist/hip area) without any effor on your part. Doing a pullup like that is harder than doing a standard pullup with your legs directly beneath you (for your arms and lats).
I guess a more understandable example of what I'm thinking is holding a sledge hammer with your hand touching the head and doing a front shoulder raise. Now, hold the sledge hammer by the bottom of the handle and do a front shoulder raise, keeping the handle in line with the rest of your arm. You've increased the length of the lever (the distance from the weight being moved from the muscles around the joints moving), so theoretically it'll "feel" heavier to your shoulder muscles. The forearm/grip muscles are the weak link in the chain (like the abs in the L pullup), but if you were strong enough in that department, or if the handle was strapped to your forearm it wouldn't be an issue.
I guess to increase the difficulty via leverage of an L pullup, you just need to (with legs straight) get your feet further away from your shoulders horizontally until your doing a full front lever pullup I guess. To make an L pullup easier (but still harder than a regular pullup for the pulling muscles) you could do them with bent legs (like hanging knee raises with a pullup).
Just thinking out loud.
Take it easy