Not sure where that 500/600 issue with the space and the non-breaking space comes from. I used fonttools to generate the xml ttx files from the 4 Charis files, the space and non-breaking space both show a width of 600.
Code:
<mtx name="space" width="600" lsb="0"/>
<mtx name="uni00A0" width="600" lsb="0"/>