But then I read that I should only use the weight of the tamper. And, it seems like that just crushes the soft ash on top.
It can be only the weight of the tamper. I can require some force. The easiest way to convince yourself of that is to answer this question: What is "the weight of a tamper"? Well... my Brebbia Pipe Nail tamper weighs in at a whopping 5g while my Peterson: PEWTER "THINKING MAN" PIPE TAMPER is 73g. One is almost 15 times the weight of the other. It's a decent starting point but it's more or less get the feel of what works for you.
