R1 and the internal resistance of the voltmeter can be thought of as one resistor, with combined resistance 1/((1/R1) + (1/Rmeter)).
The lower the resistance of the meter, the lower the combined resistance of R1 and the resistance of the meter.
I = V/Rt, so
the current in the circuit I = Vin/(R1 + R2)
V = IR
so Vout =(R1 x Vin)/(R1 + R2)
So the smaller R1 is, The smaller percentage of the voltage input Rout is.
The lower the combined resistance of R1 and Rmeter is, the lower Rout is.