Resulting from the Mecha Requirements Doc here is the PDQ Robotech character sheet that I whipped up:
Note the bolded abilities. These abilities are common to all mecha modes. If a common ability suffers impairment all modes are affected. For example, while in Fighter mode if the Speed ability is impaired one rank and is reduced to Good [+2] both the Guardian and Battloid modes take one rank of impairment to Speed. Guardian speed is reduced to Average and Battloid Speed is reduced to Poor [-2].