Mike, I agree with most of what you say but I dont think it applies to the forces a splice is under. A splice is under torsion stress and without enough surface area absorbing ( read distributing ) the stress over a large enough area, the stress will concentrate in one spot and the joint will fail. There is for a fact a minimum amount of surface area a joint must have per a set amount of stress or the joint will for a fact fail. More glueing surface area equates to less pounds of force per unit of surface area. His joint hasnt the needed surface area in my opinion ( I cant quantify that its just experience, my own, however lacking that may be compared to others ) and is likely to fail. Increasing the surface area to distibute the torsion forces into an underlay which converts the torsion force into a compression and tension, reduces joint stress and allows for better chances of survivability.
The thickness of the joint in this situation, aside from allowing surface area for glue, doesnt matter. Yes, he needs it not to bend, because working splices are much more difficult, and for certain he probably has enough thickness to prevent bending. Beyond that thickness ist a factor. The factors here that are most important are distibution of stresses and trapping that splice over an underlay.
