Earlier, John Derosa wrote:

...It would seem to me that the
forward pair, by virtue of the fact that
they are not on a parallel surface, might
receive some positive pressure. I
assume that positive pressure would be
bad for a static port...

That's not necessarily a valid way of looking at it.
I'd be inclined to look at it from a Bernoullian perspective,
and guess that the pressure there will more likely
tend to be lower than ambient.

... I should rig something up so that I
can flip between the two while in flight
to see if there is any difference in
instrument performance.

That'd be an interesting experience.

What I'd suggest is: Look in the operation or maintenance
manual for guidance about which static ports to use
for the primary flight instruments. For a certificated
glider, it may specify one set or the other, and if
so you should heed it.

On a related question, why do static
ports come in pairs? I assume it
has something to do with eliminating
errors caused during slipping in
which the ports 'see' different static
pressures.

I believe that that is it. Or it could just be an unhealthy
Western fixation upon features of bilateral symmetry...

Thanks, Bob K.