Wow! Congratulations on a brilliant hatch! Humidity obviously spot on, then!
Does the cage have glass sides? Or mesh sides that the heat can leak away through? When first making up my brooder I followed advice about using an old fishtank for baby quail but couldn't get it to hold the heat because of the glass sides, so swapped to a cardboard box with the sides lined with that silver foil stuff you can get to put behind radiators to diffuse the heat. This has worked brilliantly, it bounces the heat back off the sides so the heat lamp has a warmest spot in the middle and the heat is retained at a slightly lower temp. nice and cosy but not so hot, out to the edges. I put a max/min thermometer under the lamp area, just off to one side a bit, to see what the temp. is like in the warmest spot, and with this at about 35 the chicks are happy to move all over the box and return to the warm spot when they like. At night I lower the lamp by about 6-7 links of the chain it's suspended from, as the temperature drops several degrees once the heating goes off. the greatest danger in the early days is letting them get cold, so keep it warm and give them space to move into if it gets too hot for them directly under the lamp.
I also put the chick drinker on a shallow plate, so no water gets splashed or spilled on to the floor, because it's very important to keep the area round the drinker dry, to avoid coccidiosis.