At idle, the slides are nearly closed. Small differences make some cylinders fire with better or less strength than others, making for erratic idle. This can often be felt at the head pipes. A .5mm difference is a large contributor to charge volumes at idle position. As the slide position that is passing air is only 3mm or less. At WOT, the carb throats slides are near max. I don't recall the smaller bikes throat diameter. But, at 22 mm a .5mm difference among slides is a much lower percentage of throttle opening.
The closer you get the cylinders firing evenly at idle, the better, with little impact on WOT and mid range positions. Assuming the cylinder mechanical are in decent shape across the bank, of course.
If you are saying that a prefect vac balance at idle won't keep balance with the engine revved, You may have set the dampers on the gauges unevenly, and you have gauge indication lag. The damping screws create a storage pocket in the tubing. A damper screw that is more open than others will equalize faster than when the damper screw openings are more closed. Still, if you hold at a certain RPM and wait, the gauges should read the same equality as at idle position.
I don't set my damper valves for rock steady needle movement. I let them wiggle a bit, but set them all the same wiggle excursion. Then I use the center of the wiggle excursion as the setting point and adjust all carb position to show the same behavior.
Cheers,
