Comment 7 for bug 170835

I also heavily missing this feature!

Furthermore, I am just wondering...
when tile cloning an object the object properties "inkscape-tile:h" and "inkscape-tile:w" are added to the original object. At least in Inkscape 0.92.
Apparently, these parameters already contain the shift values in absolute units (mm or whatever page units?!). So, why not making these values available for direct editing in the "Create tiled clones" dialog?

Well, then editing these parameters with the XML editor (Shift+Ctrl+X) might be a pretty cumbersome workaround for tiled clones with spacing e.g. in millimeters instead of %.
See also http://www.inkscapeforum.com/viewtopic.php?f=5&t=18000#p95914
Let me know if I am wrong...