Actually what I meant by this is that the mobo temperature is in fact the system temp as you mentioned later, it just measures the temp of the system as a whole and not the mobo solely. Some mobo manufacturers call this the mobo temp and others call it the system temp and others call it the case temp, whatever, after all, they are both getting the temp of the whole medium inside the case itself
I said that there is nothing called mobo temp just because the mobo itself has different parts with different temp. For example, the temp of the CPU zone is different from the temp of the RAM which is different from the temp of the slots and so on. They differ slightly, yes, but the mobo has mutiple temperatures if we look at it precisely. If we are trying to get an approximation, then we can say fine, the whole average mobo temperature is 40C for example or whatever. We are just different in naming, that's it
I don't know where is exactly the thermistor that measures the temp of the CPU, but for it to be accurate, it should be very close physically to it, and for the mobo temp or system temp (Whatever) to be correct, the thermistor should be as far from the CPU as possible.