You're no less an audiophile if uncertain about your ability to detect single digit decibels of difference from vertical perfection. To confirm a setting or what you hear azimuth-wise, you can measure the differences in channel output with a voltmeter and test record.
Check this thread:
How to measure crosstalk
One place to find the Cardas test record
You can compensate for channel differences in cartridge coil voltage output by getting a level set for each channel then adjust the output with your preamps L/R balance control.