Post Note. OK the thermal mass is in the wrong place. I switched things a little adding a PC fan to improve circulation and removed the ceramic pots that bulb is in. Then added a brick under the eggs for thermal mass and trying again.
This worked really well and my temperature is now maintained within 1 degree. Again, thermal mass (aka bricks) under the eggs and away from the heat. Fan near the heat source (bulb) and away from the mass. The heat source bulb is much lower wattage worked better as well. No insulation around the eggs. A bowel with a sponge for humidity. I did have to arrange the temperature probe to be near the eggs and at about the same height or level. On 3 different thermometers this combination kept the temp within 1 degree Celsius. Even when opening it briefly to "turn the eggs". I guess, the principal here was trust the Wilhi temperature controller to maintain the temp at the source. dont add thermal mass near it. This is opposite of what you do in winter to warm coop.