Insomniac is correct in that V2, Vref and the flaps up bug speed are all three based on the Vs in the respective configuration.
At low weight, altitude and temperature V2 and/or Vref can be limited by minimum control speeds, i.e. V2 is not less than 1.1 VMCA and Vref is not less than VMCL. Adding 80 kts in that case results in a conservative stall margin flaps up. Since 80 kts is based on the ratio of stall speeds flaps30/flapsup at high weight it is conservative at low weight.