Don the only thing I can think (and this is a stretch....) is that in its first position at the back of the intake manifold, it was on the supply side of the coolant and had not had as much of a chance to transfer a lot of heat yet into the coolant as it came in from the radiator. And when moving it to the position you did in the front put it on the return side just before it exited the motor on its way to the radiator, which would allow more time for the motor to dissapate heat into the coolant and therefore cause a higher reading.

Like I said, it's a stretch; but, until I can come up with some other strange reason, that would be my best guess....

Cheers,
Dutch