You are comparing apples with oranges.When I project a logo for a client on a wall, I don't go and measure the angles, I look at the logo and see how it looks, don't need any maths to see if a logo looks good or not
The 'spec' uses scan angle as it is a constant. Distance to target doesn't matter. If we were to say 'X size at Y metres' some here might say they can't get a room with enough distance for X metres to test.
There are enough online calculators for this to be very simply calculated, so you don't even need to be a trig wizard, just be aware of its existence.
Given the math involved in show emmission evaluation, a bit of trig should be a drop in the ocean for a laser show company.
Nobody is saying you should use this to set up your show, that is something entirely different.