I'd just put it where it is supposed to be in accordance w/ factory specs if you're using factory gauges.
And add teflon tape to the last few threads of the sender. I know they're NPT and are supposed to seal bare, but they almost always weep/leak trace amounts of coolant as the metals contract when cooling down if you don't use sealing tape, especially when they are in the cylinder head where gravity favors leaking. This is why a lot of temp sending units come with sealant on the last few threads brand new out of the box. The whole myth that the tape disrupts the ground is unfounded - the cutting action of the threads removes the tape from the peaks of the threads and restores ground, plus you don't need to cover all the threads with tape.