Occasionally, I’ll export a geometry through MM exporter and the Geometry will be super small, like a tenth of the size of the original that I exported from SI 2012.
Is there a scale setting in MM or some other scale setting (16bit map scale?) that could be causing this?
MME will use the settings in the Tool palette Export menu, so if the exported model is smaller than you expect you need to check that these settings are the same as when you originally imported the model.
You can reset the Export values by importing your original model as a new Tool, then using this little plugin to copy and paste:
http://www.zbrushcentral.com/showthread.php?94752-Useful-small-ZScripts-and-Macros-for-ZBrush-4.0&p=898263&viewfull=1#post898263