I thought the same thing.
think about it this way: to add an inch on the front moves the table toward the column another inch on a Y- move. to add an inch to the Y+ the screw has to hang an inch further towards the column also. add a little more for the ball screw and mount size which iirc are slightly larger than the acme brass nut, then add a little more for the cap head screw and washer to prevent over traveling, in a Y+ move. it all adds up. 2" extra travel means more then 2" extra space from the current screw.
I follows CR instructions exactly and have ~7.5" Y travel... which I use all of I will take some pics later of the travel extremes
here is my column fresh off my buddy's Bridgeport
and fresh ON the BP
my thread has a lot of info since I knew NOTHING about cnc when I started my conversion other than it meant I could use my handwheels for christmas tree ornaments. turns out they suck for that too
welcome to the obsession, ask away!