The actual ratio varies from rocker to rocker. Racers spent their winter months measuring rocker ratios on boxes of rockers, picking out the individuals with the highest ratio.
Because of the way the lifters and pushrods point in different directions, a rocker that measures 1.50 on the bench will never produce a 1.50 multiplication of lobe lift at the valve.
Years ago Rob McC asked the question as he was putting the final touches on a design for the Erson LA rocker. Should he make it 1.50 on the bench or should he add to the ratio so it resulted in 1.50 ratio between lobe lift and valve movement. He said it would need to be more like a 1.55 to get a 1.50 multiplier.