yes the lip stop helps,,,at least for me,,, when i first made the jake bone calls i didn't have the lip stop and had great difficulty making any sounds with some measure of control. i later added the lip stop to 1 call . the stop is simply a piece of deer antler with an undersize hole drilled in it. i then used needle files to shape the hole to fit the bone. once fitted i glued it on the front only.
the new call has just a mite more length of bone behind the stop which will allow me to make some adjustments. my first adjustment is to use a 3 cornered needle file and cut a tiny groove on the inside edge of the small bone. i'll be doing that today while i'm off work.