Will, I'm in NE Oklahoma, and I catch alot of big flatheads in the early spring here. I limbline a flooded creek channel where it runs into the upper part of a lake. I start catching them about mid March, or whenever I can catch the perch which I use for bait.
Those big flats are preditors and they seem to like to hit the bait from underneath, so I don't have the bait fish very deep...a foot or two under the surface seems to work best.
The early spring here brings some thunderstorms and strong winds, and the flats are most active when there a storm coming in from the north. I watch the weather and if it looks like bad weather coming out of the north, I get those poles baited up and run em as soon as I can get there after the storm passes.