Your thermostat should open at 82 degree C . your should aim your gun at the elbow where the thermostat if located.
But don't be shy and take readings from your header tank/rad/turbo cooler(if present) this will allow you to build an overall picture of the efficiency of your coolent system and allow you to pinpoint problem areas.
It is a common issue with the 3 door re temp (overheating)due to the design of the head and it's proximity to combustion chambers. I live in Malta and all the pre-rads and coolers in the world cannot sort this out on this head design.
Keep an eye on your temps and save your car.


My Best.

Tim .