I'll be honest, I think the placement of the fan by the manufacturer is the real issue. I have never used nor seen one of these incubators in person but from the ones I have built and used for years I know that a fan does very little good at the bottom of an incubator.
Lets think this through together;
We all know that hot air rises,so without a fan at all, the hottest part of the incubator would be at the top, and the temps would decrease the lower in the incubator you get.
We also know that the purpose of a fan is to circulate enough air so that there is virtually no "thermal layering" in the incubator. SO keeping this in mind, do you not think that the fan would prove a lot more useful at the top of the incubator, blowing the hot air down and around, or at the bottom of the incubator, blowing air up?
Also, let us consider the temperatures and probe location in an incubator. Again, if you take the temps in front of a blowing fan they are going to be cooler than the air that is not moving as quickly, yes? So the temps at the bottom of the incubator in FRONT of the fan will be greatly cooler than the air above it, right?
So if you set your probe at, say 89 degrees in front of the fan at the bottom of the incubator, there is an excellent chance that, with a weaker fan, and teh cooler moving air, that the upper bins in this incubator can vary as much as 5 degrees. This is bad, agreed?
Solution: Use a fan that blows at least 15-20 CFM for optimal air movement which will eliminate thermal gradients, and place it, as well as the probe, (though not IN FRONT of the fan) at the top of the incubator with the fan blowing down.
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