I think the Origin-8 site is recommending a spindle length of 113mm ("MTN 175x48-38-28 113 SQR JIS Blk 110/74x5B 765g 3x9"), but doesn't say what chainline they are shooting for with that -- I'd guess it's the road standard of 45mm.

The ideal chainline depends on how wide your rear hub is and which cogs you typically use. Since your rear hub is 135mm (MTB spacing) then the MTB standard of 47.5 is probably appropriate. If the Origin-8 website is suggesting a 113mm spindle for a 45mm chainline, then a 118mm spindle would give you 47.5. None of this seems to match your measurements and calculations, which is a better place to start than my interpretation of a sketchy internet spec.

Did you measure from the center of the seat tube to the center of the middle ring? If so, had you tightened the crank installation bolts before measuring?

Edit: Given that the line I quoted starts with "MTN" it seems more likely that the 113 is meant to give you a 47.5mm chainline.