Hi Gary,
A narrower gap spacing as a result of the pressurized gap would keep
the arc nearer to the metal which should help cooling and therefore
quenching.
I seem to remember hearing somewhere that a pressurized gap quenches
better. I think Dave Sharpe talked about this one time, but I could be
confused. But in any case just increasing the air pressure a little should
compensate for the more conductive arc perhaps.
In any case quenching is not that important as long as it's acceptable
as shown by other experiments. In other words the reduction of gap
losses due to the shorter gap should outweigh the quench issue.
Of course power arcing is not acceptable. Quenching is heavily
influenced by spark loading, provided that power arcing doesn't occur,
and provided that the electrodes don't run too hot.
I think the better quenching of multi-segment gaps is partly due to
the higher losses in such a gap which dissipate the power and help
quenching via that mechanism.
John