I've only been through one spawning season with FHM and am not an expert. The experts will be along with specifics. But I will pass along what I think will be helpful.
Keep in mind the early spawns will be in the warmest water. The first warm water you will have in your pond will be in shallow water. Thus the early spawners will be in fairly shallow water, assuming bird predation is not keeping them out of the shallows.
I have read of FHM using a Red Solo Cup to spawn in. They like to spawn over head so they need structure with an underside. One guy that raised them commercially said he floated waxed card board (cardboard boxes like butchered meat would come in) on the surface and that was the best FHM spawning material he ever found. So we are talking ultra shallow in this instance. But they also spawn deeper.
I'm thinking in my reading 1-3 feet but the experts should have more specific details.
The structure I made used various boards I had laying around with one or two inch wood slat spacers between them and stacked as many boards as I had placed so the stack would be in the 2-3' depth. In shallow water I used old plastic waterers for turkeys and drilled a lot of holes in them with a step drill and placed them in shallow water. Also they are territorial. They will run away other minnows and fish from their spawning area best they can. In other words they will not be "group" spawning an inch or two apart. What I have read is 24" area they try to protect.
Here is a video that will give you an idea of how they spawn. It is the video I kept in my mind as I created spawning habitat for them. Fatheads breeding like crazy
A little supplemental feeding will increase spawn. At least that is what I was told by the guy that sold them to me, and they reproduced great for me.