I need an advice how to position heater

[Lziga55]

Hello, I need advice on how to install a heater in an egg incubator. I made an egg incubator with an arduino controller and automatic egg turning. It measures approximately 40cm x 50cm x 20cm. I used a cartridge heater (40W) as a heater, it is a small heater used in 3d printers. I put this heater in an old CPU cooler with a fan. Now I have some problems. If I turn the heater down (with the fan blowing down) it gets too hot directly under it, if I turn it up it's better, the temperature is even across the height of the eggs (I hatched the last round of eggs with the heater turned up but I think it's pointless, because the heat rises), and when I turned the heater to one side (horizontal), it was hotter on one side. the last time I hatched eggs only 4 out of 20 hatched because I made a mistake in calibrating the temperature sensor. And what should the fan speed be? I had it set to max, probably around 2000rpm and I know that's too much, but the temperature was erratic. I have now searched online and found that it is best to have the fan set to low speed and horizontal. What do you think I should do? And how do you have it?

 

[Lziga55]

Oh and photos I uploaded are not new, there has been shome changes, I added temperature sensor on cable so I can drop it down on eggs and I used LEDs instead of light bulb for light source