I'm about to start looking at this and don't have the answer but I can tell you the pushrod angle alone steals it's share of lift, as any deviation from
a straight line coming off the lifter results in a loss.

The more I study these, the more I realize the guys who put in .750 (theoretical) rollers back in the day....unless their rockers
were reworked of course.... I'd be willing to bet some had around .650 net lift once the lash and loss from rocker ratio + pushrod angle was considered.

I don't think the iron rockers can bend enough to lose ratio as described, I believe they would break first.