For those of you with Igloo 120qt cooler incubators a question or two

hi guys just got done building my incubator for this year and next last night to clairfy, im using a 120 qt incubator like ive seen so many people use on here in the diy stuff . i have pretty much the same setup 3 ft of heat tape, 2 cpu fans and a bunch of water bottle and i know i know im using a ranco on it right now didnt have the extra for the herp stat and i cant pull my herpstat nd off my rack till my females ovulate, so my question is where are you guys putting the temp probe on the back wall, in the egg box what? also how many of you have used it for a season with all eight egg boxes in there and what were your temp differnce top bottom left to right, also what are the acceptable ranges of temps in the incubator, everybody always say 89 but how far over that is safe and how far under as well. im just trying to get this thing workin right before i have eggs to stress about thanks for any and all help

I have used it 2 seasons in a row might use it again this year.

I have my probe directly on the heat source set so I can achieve temps between 88 and 90 in my egg box.

My differential in temps between my egg box is about 1 to 1.5 degrees.