Cylinder head temp info please

[modnrod]

Oh crap! 
I really tried long and hard to find the answer to this before asking, but without any luck.

Firstly, no, I've never used a CHT gauge, you sorta get used to the "vibes" man, and slow down when you know it's too hot. Loud clunking noises are a bit of a giveaway as well. 

But question. The usual T-couple sender place is under the plug, but the MexiBeetles have the sender bolted straight into the alloy chunky bit.
Is the MexiBeetle sender just for the EFI system, or is it used for a gauge in the cabin as well?
Has anyone directly compared the temps from the spark plug position to the temps from the chunky alloy bit?
Eg, is there a 20*C difference, a 40*C difference between the two spots, no correlation at all?
Why do aircraft seem to avoid the plug location in preference to the big chunky alloy bits?

It's all just curiosity mainly.
Thanks,
Dave

[Martin S.]

Mine was bolted onto the head stud and seems to work. It reads very low, but this motor was meant to run cool. Note the drilled fins, plus has a high squish chamber design.