The power of the scope is actually a rounded up or rounded down number. Who ever puts the specs out has some liberty to do that and marketing has a shot at it also in writing up all the good features of the scope so you'll buy it. If two scopes actually had exactly the same power and same lens size, they'd have the same fov. Some scopes have a "margin" added around the outside edges as sort of a finish to hide the seal between the lens and housing. This can take a little away from the fov if present.
I had a look on Leupolds website and yes the 4x28 is actually a 3.6x28, so I was kind of right in my thinking.
How do Wide angle scopes work?
I have at home an old Nikko Stirling Gold Crown 4x32 Wide Angle scope, and it looks amazing look look through, It seems like it has a huge FOV and and very little tunnel vision.
The specs on a Nikko Stirling Wide Angle 4x32 says a FOV of 33.2 ft @ 100 yards, compared to the Leupolds is a huge difference. Unless its only a 3.1x magnification then they must have done something in the lenses to get it like that.