the rocker arm pivots on the shaft....from the center of that shaft..the valve side is 1.5 time longer then the pushrod side...
with 1.6 rocker...the valve side does get longer since the rocker has to be over the valve stem..so the push rod side is shortened to create the 1.6 ratio...
if you have .500 lift cam with 1.5...you can actual cam lift at the lobe of .333
if you change to a 1.6 rocker...you take the .333 x 1.6 = .533...so in effect you have gain about .033 lift at the valve .....
the cam will open quicker with the 1.6 rockers...and you will have a net gain in lift...
problems...make sure you valve spring can handle the additional lift...make sure your retainers do not hit the top of the guide with the additional lift..
sometime the pushrod will rub on the pushrod tunnel in the head since the adjuster on the rocker is moved closer to the center of the shaft.....you need to check for clearance there also...