To set your jib lead position correctly, sailing closehauled, head up:
- if the upper windward telltale lifts first, move the block forward,
- if the lower windward telltale lifts first, move the block aft.
In light air you may want to adjust the proper position a little forward for fullness, in heavy air, a little back to flatten the bottom of the sail.
If your leech is fluttering with the correct jib position in use, correct it with the leech line, if you cant then the jib needs to be worked over by a sailmaker.
Certified...in several regards...