I usually see the coolest patterns from an underbase and overprint mesh that are the same count but stretched just a bit different--the neat one to me was the guy on TSF with two 110's that did this.
Always seemed to me this was usually an interaction between the mesh marks in an underbase, and where the knuckles of your overprint screen fall--but I base this on absolutely nothing but the WTF prints I've seen.
If you need the detail of a high mesh screen, try tossing Union Maxo's in your blue screens and try to reproduce this problem...
Of course, the transparent blues usually
look the best... but only if anyone's paying that much attention.