I have a young (6/7 months) albino and he's in a 30 x 30 x 30 exo terra, I originally put my heat mat at the back (wall) behind the exo terra backing but it wasn't generating much heat so I've moved it to the bottom (I stuck it to the underside) but it's still only ready 19/20 degrees c but it does feel warmed at least the substrate does.

My heat mat's only 7w could this be why it's not getting hot enough?

Thank you