Regulating Key-Dip

[mps at usol.com]

I have an old Hackley upright in which the hammers have probably 
been shaped a couple of times. I have had no problems with the 
regulation on the instrument.
However,  I think that I read someplace that the key-dip on this could 
be adjusted as low as 1/2".
My question is if I do adjust the white keys to a 1/2" key dip, how 
would I measure the black keys so that they also have the same 
amount of dip?
Also, what are the deciding factors of exactly how deep to set this 
key-dip?

Thank you

Mark D.
Montbriand