Level vials are not all the same- there are different levels (pun) of sensitivity as well as accuracy.
The straightness of the beam is also a factor. Sometimes the biggest difference between an expensive level and a cheap one is the readability of the vials.
My door level (78") is old and the vials are hard to read and only some are accurate, so I use it as a straightedge, holding another level against it- usually a Stabila torpedo one.