This is my theory re Silpat and hollow mac shells.
It acts as an insulator...using a bit of the energy and oven time to spread the heat throughout the thickness of the mat.
The pre bake resting period has caused a thin dry skin to develop...right?
This skin is exposed to more heat than the bottom therefore the top will rise while the bottom just sits there waiting for a burst of heat which will not come until the silicone mat has reached max heat saturation.
The skin has already pulled away from the bottom and nothing you can do will get that bit of batter between the bottom and top to rise up and fill the void.
I have a boxful of the Silpat brand mats.
They are great when I need a non stick surface for sugar and gumpaste work.
For anything else I use parchment.
Comes precut in the most common sizes.
Yes I am an insomniac.
Have to have something to do while waiting to drop off.
So I ponder the mysteries of the universe lol.