Always check your withholding with this tool if there are personal or financial changes in your life that might change your tax liability, for example new employment or a promotion changing income amount, or new family members altering the number of dependents you claim.
believe the answer you're looking for has to do with the pressure-altitude-voltage derating related to corona discharge, which increases (gets worse) with higher altitude and peaks at around 80-100,000' Typically this is considered to occur at votlages above 300 V peak, but be sure you are accounting for all transients and internal voltages.
Topographic cross section showing the effects of urban air pollution on precipitation as the clouds move from the California coast east to the Sierra Nevada Mountains. Maritime air (zone 1) is polluted over the coastal and Central Valley urban areas (zones 2, 3): no precipitation decrease occurs.