The 'Field of View' is really a lot harder to measure than one number would indicate. Consider the 27 degrees as sort of an average.
An object is said to be in the field of view when it returns enough photons that the sensor can detect it.
The flash of light goes out in a cone slightly larger than the FoV. (Look for 'exclusion cone' in the dats sheet.) The light hits an object and bounces back.
So take the case an object just entering the FoV.
If that object is very reflective, it could enter the FoV only a mm or two before being detected.
if a similar sized object was a very dull black it would have to be very far into the FoV before enough photons were detected.
And then there is the issue of distance.
Very near objects return a very strong signal as the light dissipates as a square of the distance.
So very near targets would be detected with only a mm or two into the FoV.
So, in truth the FoV is dependent on the reflectivity of object and the distance.
Different sensors should be very consistent, provided that your test is identical.
I'm going to guess that your results were due to changes in reflectivity and distance.
Try this... Get some retro-reflective material. (it's sold as 3M reflective tape although there are many vendors). It is amazingly reflective. And it returns the photons in exactly the direction from which they came. Use that to establish the largest possible FoV at some large distance - a meter or two depending on which sensor you have) Then try the same experiment with a sheet of cardboard at a 'reasonable distance. (50% reflective and easy to get.) The cardboard represents a 'common object'. Then try again with that same cardboard painted with flat black paint. (5% reflective, and your worst case.) You could also try printer paper. It's 88% reflective, and the upper bound of 'reasonable' objects that you might encounter.
This will give you the full range of possibilities.
Use this data to make your assumptions about your situation.
Good luck,
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