Yes, that rod that slides behind the foot pedal does a full travel, from low to high.
And yes, it is nearly exactly 1.5" of movement on the external rod from top cable position to low when my son steps on the pedal (and I'm under the car measuring).
I do believe that adjusting the external rod on the pedalbox spline could get me a wee bit more travel. I am going to try that first.
I have a serious phobia of working under cars unless it is on a lift... but I'll try to slip under there next weekend and see what I can fiddle with.