The "true" rocker ratio on stock cast iron rockers is all over the place. Back when I was limited to running those , I made a fixture to check which ones gave the most lift . Some were as high as 1.62 ratio but most were in the 1.55-1.58 range. Stephen is right in that pushrod length itself does not give more lift. It's more like the wrong length ( and attending poor geometry) LOSES lift. In other words if you have a cam with a .305 lobe lift and a true 1.6 rocker ratio with "perfect geometry" and zero lash , you would get .488 lift at the valve retainer. IF you get less than that at the retainer , the rocker ratio is off or the geometry isn't right. Obviously valve lash changes every thing as far as actual lift at the retainer.
'66 GT350H-3 time cover car - Car Craft July'77,Modified Mustangs and Fords Feb2011 ( w/article), Mustang Monthly June 2014. Bracket raced by me for the last 44 years. Yes it is a real one.
'68.5 R code GT fastback
'67 Ranchero 408W -427 glass hood
'78 F350 "Oleynik" car hauler
Ford Experimental parts collector