I was curious about the question so I looked it up.
The Correct name for the Pictured tool holder is a "Weston" tool holder. ( According to the ninth edition "Workshop Practice" 1947.) A British publication
This reference also refers to the angle in question specifically as "front rake" and that top rake is the angle of the top of the tool relative to the radial angle from surface to center of the job. Which would mean that top and front rake are only the same angle at center height.
So for tools not on center height, Lower gives less top rake, higher gives more, but the front rake remains the same- (I guess there is a quick cheat in there for cutting brass if all your tools are set up for cutting Ali - I haven't tried it.)
The Bad news is this particular book doesn't say what the standard angle should be on a Weston toolholder
I guess Weston is a brand name - are they still around?
Bez