Well , why 4'9" back from the firewall you ask .
Simple 5' put the transition back to carpet ; already said that , 4'6" put the transition under the passenger seat pedestal and 4' was under the drivers .
4'9' made for more cutting but I used up the rest in the step well.
Started with the tiles at the top of the stair well , that put the edge of the forth row at the side of the steering column floor boot, and made the cut out for the foot valve easier . red arrow in picture .
A note , years ago I noticed that the drivers seat was not centered to the steering wheel , I believe this was done for clearance to the slide flange with the power seat was fully moved to the rear , that was not really required , so I re-drilled the pedestal to move the seat , the off set was bothering my shoulder on long drives. re-drill shows in one picture. You'll have the seats out so you can decide if the mod is necessary.
Both seats had sunk into the sub floor so have leveler compound handy , and 1/2" plywood to level the throttle pedal, longer lag bolts to re-mount.