A quick google search gave me this info. Now I know not everything on the internet is reliable but this makes complete and perfect sense to me. Not to mention, with a bio set up I would assume you will need over head lighting anyway to help with plant growth and maintenance?
Sounds very complex if I'm honest, but if you've got a strong plant/ soil/ substrate knowledge and a strong knowledge of the needs of your reptile then by all means to ahead!
Have a read
Heat mats aren’t very compatible with bioactive or naturalistic setups.
Heat mats are traditionally mounted to the underside or bottom of an enclosure to provide heat from below. This is an effective way to create a warm basking surface…until you have several inches of soil or other substrates on top of that heat mat. Even with a thermostat probe placed on top of the substrate, chances are that your heat mat simply won’t be able to produce enough heat to get through all of that substrate for your reptile to benefit from it. The result? A hot heat mat and a cold reptile.
Plus, if your terrarium is planted with live plants, the heated soil can potentially damage or even kill your plants’ roots! It can be hard enough to keep plants alive and thriving in a reptile terrarium — why make it harder for yourself?
(As a side note, the strain of trying to heat through all that substrate can lead to scorching of the surface underneath your heat mat, whether it’s wood or plastic. In extreme cases, it may even cause a fire!)