Angelcare wood under matress Q

Hello Girls, Yet another question on the angelcare monitor, thanks in advance for any replies! On the angelcare web site it says that the wood to put the mat needs to be 400mm x 600mm x 6mm (16"X 24" by 1/4") To thoes who got a bit of plywood what size did you get?

To be honest we didn't put any wood under it we just made sure it lay flat across the slats of the cot and we had no problems with it.

I never knew that as already said we just put it between slats of the cot wood and it always worked perfectly.