How effective is back heat compared to belly heat?

I'm sure it's effective or else it wouldn't be so widely offered by people selling racks but I'm curious how effective it is compared to belly heat when it comes to aiding in digestion and keeping overall temp in the tub warm. Do you still have issues with the ambient temperature in a rack or do you keep the room warmer? I'm looking at different plans for my 1st build but ambient temps are a problem in my house. Currently, I have a CHE on a dimmer to help keep the ambient temp up but that won't work in a rack for obvious reasons.