I'll preface this with saying I'm short. 5'4" and I have three aiders by backwoods. All three are 3 step aiders and each step is 13". I did that because if I use all three sticks I can get 18' to my platform. 5 1/2' between stick placements is what I do and I'm able to get to a decent height.
However, I use the one stick. I actually have 4 sticks with three step aiders. 1 muddy pro, 1 EWO ultralite stick, 1 shikar 17" and one 1 mini shikar with a scout platform on top and double step on bottom. each one has a three step aider...and either one of those sticks I can one stick up the tree. I think the 13" step is perfect as it gives me about 38" to the bottom of the aider to the bottom of the step then what ever step combination I have I can advance up the tree.