If you are small meaning slim, be careful buying these long underwear, the appropriate size tag for the small is Medium, it would be still large for Medium. The leg height are fine, the waist looks ok, but its make for someone with large belly and it wouldn't work for someone  with flat belly. Not sure what to do with them really. The fabrics are really good but that it.
Honestly they should start make an XS sizes for people who are not obese or overweight.
If you are a big guy they are right for you but if you are small or slim I wouldn't recommand these for you