I'd be curious to see a screen shot. I've been finding lots of smaller catfish mixed in the areas I've been finding white bass and sometimes telling them apart can take some practice and may not be super obvious.
Smaller catfish have a very rounded narrow arc similar to an individual white bass (vs a decent to large catfish will be flatter arc with most the hardness on one side. One of the key differences is their behavior. One key difference is that white bass usually school very tightly and appear more as clouds on the bottom. Catfish are loosely related and not cloudy. You can usually sit there and count each fish. Their school mates usually are loosely related and suspended throughout the water column as well.
As far as presentation, a good vertical presentation is probably the way to go. You can try catching them "smoking the reel" by letting a slab go to the bottom of the lake and then reeling as fast as you can straight up. If they don't respond to that tactic, let the slab go to the bottom, reel up the slack till your rod tip is almost touching the water, then slowly and steadily raise the rod tip up as high as you can in within five the six seconds. I do both these tactics under my transducer with chart speed at MAX. This allows me to see the fish and their reaction to my presentation.
Hope that helps some!
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