The Bytes column of the output of whos does not tell the "truth, whole truth, and nothing but the truth" for certain situations.
A and B do not necessarily point to a different block of 80,000 bytes due to the copy-on-write behavior of MATLAB.
This does not list the full amount of memory required to store all the data and properties associated with a figure window.
Use that data as guidance, not law.
And no, there is no way to get the actual amount of memory associated with f (maybe walking the list of properties in a MEX-file, but again things like copy-on-write would complicate even that.)