Frankly I’m not sure how I would determine that. Usually I use hold down pins to hold material as flat as I can to the honeycomb. I did the same here, but the material is pretty thick and I could not tell if beyond the edges being held down, the rest of the piece didn’t dome upwards.
It seems pretty flat - the pieces I’m using are cutoff’s from some shelves I built for the storage room in the basement and they sit flat on my table saw, so I’m assuming so…