Yes, dont want the probe in the egg tub. This causes problems with the air outside egg tub being Higher than set temps. Thus causing condensation problems when eggs are in the tubs. Which doing it this way for one clutch is fine, but if you have many it can cause other eggs to have problems.
I always attach mine to the lowest shelf handing in middle away from the flexwatt. Doing so you should notice a steadier temp top to bottom.