How made different value for each side in random effect? Example side A -15% side B 40 %

Case in point... the random feature doesn?t produce a consistent offset from the edges. If it did, it would?t be random, it would be negative pull compensation or whatever it would be called.  The value just sets the threshold within which the stitches travel to the edge, each one a different length, each one a different needle penetration spot. That?s why it?s called jagged edges. 

In fact, if you have an object with random "on" and don?t change anything to that object and just regenerate it, it will produce a different set of stitches than the one before - even though it?s the same object, even though you didn?t move any nodes or change any settings. 

If you need a perfectly consistent randomized placement of stitches that endures any future changes, you need to do the way we did animal fur 20 yrs ago, before the auto features became available - one stitch at a time.