dont remember detail...too much to remember. but basically anything above 18 the stock turbo moves out of its efficiency range. I think it produces more heat than power.
K&N makes A/F monitor? wow, never heard of that!
does it use wide O2 sensor? you should get one of those that reads out A/F ratio in #s so you know exactly where you are at. green, red and yellow just dont cut it. its like saying "the car felt faster".
you should be around 11.5-12:1 range. no higher. anything below 11.5 is probably a BPU running without a fuel controller (too rich).