Tern probably doesn't recommend it because it really doesn't fit. Looking at the pictures it doesn't look like the Short Haul has the mounting points needed for the Spartan so while they do make a 100mm version of the rack it looks like it isn't designed for that bike. However get one of their many awesome front racks or baskets and you can carry a ton of stuff on the frame really nicely. Those Transporteur racks are awesome hold quite a bit of stuff (I have piled them high in the past)

I am curious how and why someone put a 74mm rack on that bike as I believe they are using the same forks on both. A 100mm makes sense aside from the lack of mounting point unless maybe they put it up higher on the fender mounts which may make a little more sense if that fork as a higher axle to crown but haven't really measured between bikes that it would actually fit on vs. the S/Q Hauls.