The stock needle is 3 tapers. It starts with a very short straight section, progresses into a rich first taper, then an alight mid, and the last supplies good fuel towards WOT.
The problem is that the short straight means the diameter has very little effect. Most people turn the idle screw in so far that they are actually fuelling from the first taper. The first taper is rich which gives poor throttle 0-1/4 throttle so most will lift the clip to lean it out, which then sets the second taper up to be too lean when opening the throttle more (as you typically do under loads).
Going to a different needle with a leaner first taper lets you drop the clip position richer to give a clean bottom end, without falling lean in the mid. Top is around the same.
With your half clip leaner in the same clip, it just made you leaner, which is why the plug read whiter.
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