The Sage is a 62" bow, and should not stack at a 29" draw, so something else might be going on. It does, of course, continue to increase in draw weight the more you draw it, 2-3# per inch of draw, as all bows do. So if you draw it 28 1/2 one time and 29 the next, you will feel a difference in draw weight.
Of course, it is possible that something could be wrong with that particular bow, but stacking at 29" should not be a problem with the Sage in general.