There are many reasons why a sponge might shrink.
-One reason could be factory tuning.
-Another reason could be that, sometimes when a person puts the rubber on they roll/press it to get the rubber pressed on fully and that stretches the rubber.
But, you should know that the sponge on a TT rubber is not all that different from the sponge you use in your kitchen. If you poured water on a kitchen sponge, you can see it expand. If you pour water on a TT sponge, it will also expand. Water Based Glue is in fact glue and water.
When you pour WB Glue on your rubber, liquid from the glue does cause the sponge to expand a little.
So brokenball is 100% correct in what he has said. And it is worth letting the glue dry before you put the rubber on the blade.
BTW, old, classic TT glue which was basically rubber cement, and speed glue, which was basically rubber cement with a whole lot more VOCs added, also have a liquid component. The liquid component is the solvent which is the VOC. That liquid evaporates much faster and fills the pores with VOC gas. This is why speed glue cause the sponge to expand so much and play so much better: more gas in the pores of the sponge. And why the effect of speed glue wore off so fast: 6-24 hours.
So lots of things can cause a rubber to expand before it is glued on or shrink after it is glued on.
Edge tape won't change that. But it will make it so you don't see it or focus on it. So it might be of some use.