Warning, I've had two strong cups of Joe, and no breakfast. This post may be a bit disjointed.
Aahhhh haaaa....good illustration Jack
If I get it right, the more friction where the rope goes over the TIP, the less load on the TIP, so in a tree we'd never really experience a true doubling of the TIP load with a base tie because of the inherent friction of the rope over the limb...did I get that right?
Its absolutely, physically impossible to see exactly two times the load.
All of this is very demo'ed with a branch and a string . For a demo, you can jab a cut branch into the ground to 'plant' your 'tree'
Then base-tie, or trunk tie. Directly (like a 180* scenario), and with lots of crotch redirects. With more excurrent and more decurrent branches/ trees. It will be very concretely experienced, I think. Shock-load the system. Pull to failure. Rig onto it. Whatever. You could use a climber (any weight or toy figure) on the end of the line so you have an constant force (weight...this is a vector force, btw). Hang a 'log' on the rigging line and drop it and watch.
Because I have a BASIC background in this type of physics (year of hs, year of college at an engineering school), and thinking rigging for rock climbing and tree work, I can read diagrams pretty well, as it pertains to me.
It is pretty abstract for some people. Most people experience and can 'read' the force on the line/ base anchor/ redirects, etc in a demo visually and with feeling the pull on the line or tree or whatever.
I suspect that it will do any treeworker well to have a basic, formal concept of vector forces (and friction wouldn't hurt with lowering devices and friction hitches).
Mark Chisholm wrote a good 'Article' on TB about Engineering a Tree Removal. Good diagrams about vector forces.
Jack, looks like you made a good diagram there. Can you make the arrow represent vector forces (i.e., as the force is less, the arrow, which represents the amount of Force and Direction through arrow length and direction would be shorter)?
I think that would more clearly show the forces.
As Erik points to, be conservative (think higher forces) than actual for a cushion.
The more static your rope is (htp, etc), the more you have to consider a shock absorber (Screamer, or the like).