I have electricity in the coop so I brood out there as soon as they come out of the incubator or arrive in the mail whether it is in the middle of a summer heat wave or below freezing in winter. My brooder is 3 ft x 6 ft (1 m x 2m). Brooding outside brings a special challenge because daily highs and lows can vary so much. Instead of trying to keep the entire brooder the perfect temperature I keep one end warm enough in the coldest temperatures and allow the other end to cool off enough even in the hottest temperatures. In the winter there may be ice in the far end of that brooder but the heated area is warm enough. Even straight out of the incubator I find mine are really good about self-regulating temperature is they have a choice.
If the chicks are huddling at the heat source and never roaming around, they are too cold. If they are lined up as far from the heat source as they can get, they are too hot. As Azygous said, hot can be as dangerous or more so than cool. You adjust the heat by raising or lowering the lamp, changing the bulb wattage, providing a bigger brooder, or providing better ventilation.
With all that said and looking at your photo, I don’t see a problem. They are not lined up as far from the heat source as they can get. They are a comfortable distance away. I think you are doing OK.