Multiplex based autoscale, question on simple circuit
Vref is the new 0V and this is where you are getting confused. 

With 1V going in with a gain of unity (Rf = Rin), the voltage out is: -

\$V_{OUT} = V_{REF}-(V_{IN}-V_{REF})\cdot\dfrac{R_F}{R_{IN}} = 2.5 - (-1.5) = 4 volts\$

This is an offset from 2.5V of +1.5 volts and remember your input voltage of 1V (relative to ground) is actually -1.5V relative to 2.5V (the new 0V) i.e. the gain is -1

With 10V going in, relative to the "new 0V" the actual input is +7.5V (bear this in mind) so, when you do the math with Rf/Rin = 0.1 you get an output voltage of 1.75V or -0.75 below the "new 0V" of +2.5V.

So, relative to 2.5V you put in: -


-1.5V at a gain of unity and got out +1.5V and
+7.5V at a gain of 0.1 and you got out -0.75V


Does this now make sense?