While we are on the subject...I initially misunderstood blinddrew’s last measurement and measured the distance from a straight edge across the frets over the top of the pickup. 6mm neck side edge and 5mm bridge side edge. Take off 2mm from the bridge side (I think 1mm could be sanded off the neck edge to sit flatter) and we have a length of 7mm plus the extra length associated with bridge height and nut height/fretted string position.
As a side note I had no idea how strong the pickup magnets were until I tried to use my metal rule as a straight edge for the above measurement. Smack! No wonder you don’t want the pickup too close to the strings.