Replace thermostat or replace fan switch?

[64stpside]

Hi guys....
I've been working hard on my 64 s.side, (pics forthcoming). It's got a stk 305. I installed a new radiator and electric fan along with the fan wiring kit (non adjustable). The kit has the fan switch that screws in the head/intake. My intake has no provision for installing the switch in the intake and I have the sensor for my mechanical autometer temp gauge in the driver front head so I installed the fan switch in the rt rear head. The switch temp range is on at 200deg and off at 180 deg. The fan comes on right at 200 but wouldn't turn off. After about an hr trying to figure what's wrong, I realized when I did intake gaskets a few months ago that I put in a 190 or 195 thermostat....there's the problem. My 1st thought is to put in a 180 thermostat but I wonder if the fan switch being that far away from the thermostat housing will not see 180 deg coolant as it travels through the engine.
So, thermostat or adjustable fan control?