I am very surprised by the suggestion of more than 2 stops compensation for a circular polariser at the full setting. The maximum should not be any more than +1.5 or +1.6.
Hand metering with a baseline calibration of the filter factor is the most reliable and takes away the known hit-and-miss of TTL meters. A hand meter will also allow you to rise above the undesired effect of completely flattening illumination (resulting in a dark, flat and overall unsatisfactory exposure) by analysing the light either with spot- or incident metering.