O.k: and one more test with Fusion360 and T-Splines.

However i must admit that i did not checked for proper scale settings,
like mm or cm so...

Size: 999,83x999,77x999,78

Edit Size:

x: 999,8378
y: 999,7943
z: 999,8120

Now when doing the same procedure with setting x,y,z to 100,0000
the model size stays the same.

P.S. for those who use macOS Fusion360 needs an OS upgrade by
January 2019, according to an alert, when i logged in to Fusion360.

So this was it then for me with Fusion360 usage, because my old
iMac does not support Mojave and i don plan to buy me a new iMac
soon...

Regards
Stefan