The sensor may not be as helpful as you would like. Mixture distribution, even in a stock manifold, varies between cylinders much of the time, and (worse) the degree of difference varies with RPM and throttle opening.
If the sensor is in the headpipe (after the merge of all cylinders), a meter is going to give you the average of all conditions, in which all 6 equal will look very much like 6 all over the place but in different directions.
Remember, you're tuning for the 1st cylinder to knock which means hottest, leanest, and (probably) the loosest quench clearance.
