Take your point about 142 being higher than 105, but if you progress your point then is a 180 degree angle (I.e. pole and elastic pointing straight ahead, like in pic 3 above) an increase or decrease in angle from the 90 degree right angle when the fish runs along the bank?

The more acute the angle, (and lower the number), the greater the angle. Increase the angle and the number goes down, and vice versa, at least until you go past 180 degrees.

Also, I think your calculations miss an important point about the distance a fish moves . The angle will change depending on distance from the pole tip, unless you’re fishing the mudline and the fish runs at a direct right angle and doesn’t come away from the bank.