ARC tube biasing

 I noticed that in the manual of the ref75se, it explains that when biasing the amplifier, for best results, voltage should be at 117.5. The voltage in my home fluctuates between 118-119.5.  Would it be best to peg the the needle to about ever so slightly onto the positive side of the window past the bias target line to slightly compensate for the higher voltage, therefore theorically hitting the proper bias point when and if the voltage were to be 117.5? Or should I bias to hit the target line even though my voltage is higher than 117.5, and in actuality 118-119.5?   Splitting hairs?