I am not really sure that I understand your question, but I will venture a guess anyway. As far as ideal drawlength of a bow for a given bow, that only matters if their are big differences in the amount of energy stored per inch drawn, and that will vary with every bow model. Alot of bows start to stack slightly after 29" or so depending on the length, but that will really depend on the style and length of bow. As far as a thumbrule for poundage changes, a pretty close guess is take the peak draw weight at a given length, divide it by 20, and that is around how many pounds the draw weight changes per inch change in one direction or the other. For example, a bow that is 60# @ 28" should be approximately 63# @ 29" and 66# @ 30", 57# @ 27", and 54# @ 26". This holds pretty well for a couple inches of difference.