They can grow quite a bit, but usually that means they are taking on too much water. Eggs that grow too large, usually drown during hatching, also the embryo's actually tend to be smaller. If the eggs are firm, no indentations, white and fungus free, no discoloration, then your in good shape. Its not uncommon for eggs to make it the entire incubation period, only to die while hatching because of to much contact with moisture or improper temperatures, so there aren't any guarantees. I've had the best results with keeping them at 83, and making sure they are buried 75% of the way in the substrate. For the substrate, I use a mixture of vermiculite and water 10 to 3 by volume, kept at a very high humidity being careful not to allow the eggs or the substrate to come in contact with the condensation.