Christian and Sergej either one can chime in.
JK. The tech drawings all show the 19.7 mm version. That explains why there´s no difference when you put them side by side
The number indicates the length of shaft from the underside of the headstock to the string-hole (is that even a correct word
Just measured two of my Imps with a caliper and both have the 23.7 mm version. I´d say the different heights are due to different headstock measures. Either way, you should be on the safe side with the 23.7 model.
Hope that helps.
Practice cures most tone issues.
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