Going back to lego, lets say we have 3 lego pieces. small (25mm), medium (50mm), tall (75mm). The small needs 1 degree, medium needs 2, tall needs 3. If there was a forth part measuing 100mm tall, the draft would be 4 degrees. Super simple rule of thumb. For every 25mm of hiehgt, add 1 degree of draft.

It makes perfect sense if you think about it, the taller the wall, the more surface area, the more surface area, the more friction. More friction means that a heavier draft angle is required to releave the higher level of friction.