The force draw curve, even on a trad bow, is not a completely straight line. A bow will gain weight a little quicker early in the draw, then a little slower toward 28 inches or so, and then start gaining quicker again somewhere beyond that. (Where it starts to feel like it is "stacking") That curve will vary slightly from one bow to another based on limb design.
But the amount it gains per inch is more a function of the draw weight of the bow than anything else. A heavier bow will gain more pounds per inch.
As an example, a bow with the string 8" from the the back of the bow while at rest, (about a 6 1/4" brace height) must be drawn an additional 20" to reach 28". So a 40# bow will gain an average of 2# per inch. A 60# bow will gain an average of 3# per inch.