buck regulator Vout configuration
You want an output of 1.3 volts but you must have 1.231 volts across R1. This means R2 has a voltage of 1.3-1.231 volts = 69 mV.

Given that current thru R1 = current thru R2, R2 must be smaller than R1 or, put another way R2 = \$\dfrac{0.069}{1.231}\times R1\$ = \$\dfrac{R1}{17.84}\$