The depth that fish sit at will vary each session. In fact, it will almost certainly vary throughout the session as the shoals go up and down the water column. I always start with my rig set 3ft deep but I will change this throughout the day. I don’t just guess when a change is needed and there are a few indications that will tell me it is time to adapt. If I am getting no bites or movement on the float I know there are no fish at the depth I am fishing, or above. This is because I would be getting bites, or at least indications, on the float as fish brush up against the line. When I am getting bites but can’t hit them or I am foul-hooking fish it is time to shallow up as this tells me the fish are above the rig. I adjust my rig by 6in intervals until I start catching well. You might get a run of fish at one depth and then have to make a change to relocate the shoals. So, always be prepared to change depth.
Tommy uses Method Feeder Stops to fix his float position