That's a chicken cooker, not a chicken brooder. They're in the far corner and can't get any farther away from the heat if they need to.
When I brood chicks inside my house I use a 45 watt bulb in one end about 8" off the floor, shining straight down. If they pile up I lower the light an inch or so, if they scatter I raise the light an inch or so. When they're in a loose little group they're just right. I've never used a thermometer in a brooder.
I use this same method in totes inside my house, as well as in brooders and wire cages outside.
Hope this helps.