Hi,
In a Hyperion 17mm that is about 20mm from the glass, or about 5mm above the (not rolled down) rubber eyecup, which is 15mm length. When rolled down the eyecup edge is about 4mm above the glass.
In a 8mm Hyperion it is clearly less, about 15mm from the glass, or about level with the eyecup.
In a borrowed Televue Ethos I have for a bit, it is also about 15mm from the glass.
http://www.iceinspace.com.au/42-286-0-0-1-0.html
http://www.ozscopes.com.au/william-o...eyepieces.html
These WO EPs are specified to be 20mm eye relief. Maybe someone can give you a report?
Cheers