How to limit current using voltage regulator
For anyone curious about the solution to this, I'll post it here.

My first mistake was not knowing that the input voltage must be at least 2V more than the output voltage.  I just thought it had to be more, and because the output was the 6V I needed, I assumed that an input of 7.5V was ok.  In any case, the current limiting wasn't working as I would expect.

The second problem was that when I modified the load so that I could use my 200mA Ammeter to measure the output current, I ran into the problem that the current limiting of this particular voltage regulator doesn't work that low.  So again I couldn't detect any current limiting.

My next attempt was using an input of 9V and drawing about an amp under steady conditions, and here I could finally see the current being limited and finally see the effect of adjusting the potentiometer.  And so here I was able to answer the questions about which way to turn it and how to explore the whole range.  So turning dozens of times past the end is not a problem, and you don't have to turn dozens of turns back again to get back to where it was.

Unfortunately this wasn't quite the end of the story, as my actual load contains motors which draw a large current at startup - this is the inrush current which I was trying to limit.  Even with my current limiter set appropriately, this start current drew a large spike of input current into the regulator, and the current limiter apparently still wasn't fast enough to react to the spike in time.  So the input current spiked beyond the power supply's short detection, and the power supply still cut out to protect itself.

The final solution was to feed the regulator with 12V instead of 9V, which reduces the input current.  So even though the input current still spikes, it no longer reaches high enough to trigger the power supply protection, so the motor stays powered and gets past the startup phase.  With the right adjustment of the second potentiometer, the steady state output current is fine and during the inrush spike the input current isn't too high.

Thanks all for the help.