Here is an older shot of a nice sandy bottom (really constant gradient) with some YT cruising through about to crush my three-way setup and "ruin" a day of halibut fishing
The hard/soft return appearance is going to be dictated a lot by how you set the sensitivity and colorline on your personal sonar. Once you get used to reading your sonar and get it dialed in to where you can see clear marks in the column without a lot of interference, start bumping the bottom with a 10-12 ounce dropper loop. You'll be able to tell if it's hard or soft, especially in shallower water, and then you can start correlating in your head with what's marking on the sonar.