an STL does not does not contain the info like if you set it to mm,cm, or inch. Your program stores that info as a percentage of a meter, which the stl does contain.So you modeled it at 100 mm tall, info for a stl would be .1 tall. So selecting meter at upload it would be printed at .1m=100mm height.
Now if you export it as a dae, which SW does recognize those unit measurement settings ,you have to set no unit at upload, it is printed dimensions you model it, mm,cm,inch.
The values of .76 and .86 you got in NF was correct, NF justs adds mm. if uploaded in Meter should work out at at mm 760 x 860 or cm 7.6 x 8.6. Obj file behaves like a stl by the way for uploading to SW.
Good news, if you upload a model for color printing, all you have to do is export the vmrl, pack with the texture, chose METER again at upload.
Keith