Has anyone, that has cooling fans run from a switch, notice if eng temp will rise if fans are turned on while at highway speed?

I have 87 TPI in my 82 Z-28.
The primary cooling fan is controlled by the ECM which has a custom prom.
I control the secondary fan relay with a switch.

When I burned the prom I originally set the fan to come on at 195 and off at 190. When I tried it out, the fan came on at 195 but wouldn't go off, even when eng temp dropped 185.
By expermenting, I found that the "on" and "off" temps have to be at least 15 degrees apart, not sure why.

Anyway, I now have the fan set to come on at 205 and off at 190.

When driving at slow speed, eng hits 205 and fan comes on. When I hit the highway, the fan stays on and eng runs a little hotter than it did when I had manual fans (turned off).

I'm now thinking that on the highway, if the fan is on, it's actually blocking some of the flow thru the radiator.
Due to my background in aviation, I know a rotating fan blade creates a LOT more drag than non-rotating fan blade.

Thx

 

bingo, the fans will decrease airflow at speed(anywhere above about 35-40 MPH), which is why i dont wire my fans to be on all the time, i have just lowered my on/off temps

at the track, i unplug my A/C compressor and turn the fans on in the pits by putting the **** to A/C