| I haven't spent a lot of time exploring this, Steve, but I have noticed some similar things. I'm not sure it's a setup issue.
My thoughts are that a plucked string's pitch starts to decay immediately, faster or slower depending on the string, but still starts its pitch decay right away. A bowed string does not. That could explain what you are starting a pizz note a tiny bit sharper than a bowed note. By the time your ear acquires that pitch, it has dropped a bit. Just a theory.
Another is that the weight of the bow can change the length of the string, whereas with a pizz'ed note, as soon as it is released, the string is free to osculate back through it's original position. We know that the length of the string is one of only a few things that do influence the pitch. Try experimenting with different bow weights to see if you can effect the pitch from a consistent left hand position or open string. I can and my arco technique is not consistent enough for me to do it on purpose, while I'm actually playing something.
Just my thoughts from having wondered about this before. I could be way off base.
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