How old are the sails?
Using a forward lead like that will "close" the leach a little, and may be symptomatic of a baggy or blown out head of the sail. I guess, the next question would be how close to the wind can you point, and can you tack through ninety degrees or less? Normally, you would lead the jib sheet further aft when pointing as high as possible, but it sounds like when you do that, the head of the sail probably luffs. A good starting "neutral" point would be to draw a line from the midpoint of the luff of the sail, through the clew. Extend that line to find the position of the block. When sailing higher, move the block aft, and when sailing lower, move it forward. If you can't get the sail to break evenly when doing this, I would wonder a little...or maybe a lot! Good luck.