As the tobacco "pluffs up" whilst smoking, I give it a tamp, but I don't press down. I let the weight of the tamper do that. In this way, the ember is kept in good contact with the tobacco in the bottom of the bowl, but I'm not mashing ashes into the tobacco.
I also use this tamper/pipe tool, and it has a nice heft to it:
I also use this tamper/pipe tool, and it has a nice heft to it: