ja, the technique can be done in most water speed and depth, but my preferred water is usually at walking speed and the depth is usually from as shallow as 2/3 feet to 6 feet. In shallower water (2, 3 feet), I look for slightly faster water with some chop on the surface. This suggests that the rocks on the bed vary more largely in size than flat water. It provides structure for the fish. In deeper water, I prefer to fish in slower water. In fact, the spot where we have been fishing, the speed almost does not exist. This really allows you to drift the roe longer, and prevents your bait from falling off the hook when retrieving it. The bites are also very precise, so easy to spot.
You can certainly float fish in faster water, but as Cohoman said, you risks having your bait being washed away by the current and the amount of your drift time is short. I like to have my bait going through my fishing area for at least 10 to 20 seconds. That being said, in faster water, the fish usually grab it with no hesitation so the float dive is much harder. These fish are rarely missed.