I read on another site that crosses are typically 32-37% looser than the mains even though the ideal difference is 20-25%. When you weave the crosses and tighten them, the mains tighten up because the weave stretches them. Also, when you apply tension to the crosses, the friction from the mains reduces the amount of tension that is applied to the string.
The article suggested that you can add 4 pounds to the crosses, or if you have a constant pull machine, you can wait about 20 seconds before clamping (and you can weave the next cross in the meantime). I'm doing the latter.