Loop to loop joints in close sized mono should not create a hinge point of tightened well.
We have some "nail knotted to the line" butt sections. They work fine.
We also use some braided mono loops (home made) and we do NOT use heat shrink tubing. We use a nail knot (ONE) instead of the tubing and if we glue, we glue ONLY the nail knot so as not to inhibit the "finger sleeve" principle.
.....lee s.