1) Scintillation or stars appearing to flash at the periphery of our vision
shouldn't have too much of an effect on your ZHR's for major showers...unless
you do it often.  With minor showers, where rates could be in the realm of 3
or so/hour, a ZHR can increase more than it should with just a few
scintillations. Sometimes scintillation effects will occur right in the
middle of your view while making a star count. These occur because a certain
number of photons are required to trigger a neuron to fire and produce an
image within our brain. For very dim objects, your neurons will store( for a
limited period) the photons until they reach a threshold.  Afterwards they
fire and the image briefly appears.  To see the object again, the buildup
will have to be repeated.  But the major thing to remember... if you're not
sure it was a meteor...don't count it. And making a star count where you have
to count dim stars that are only seen when a neuron builds up gradually to
reach a threshold...well I wouldn't count these.  If you saw a meteor as dim
as the scintillated star, you probably wouldn't see the meteor. Thus on paper
you would be working with an unrealistically high Limiting Magnitude. 

2) When you make star counts for your Limiting Magnitude determinations, you
can use averted vision...but don't struggle too hard to accomplish a count.
 Count a dim star if you can do it without extreme difficulty.

3)One's center of view should be in an area that's about 50 - 70 degrees
above the horizon.  Ideally about 30 degrees from the radiant.  This is not
always possible for various reasons.  During a full moon, LM's much above 5.1
is very difficult to achieve...particularly if the moon is directly in one's
eyes.  For most of the major showers that occurs during a full moon, I find
the darkest part of the sky (after midnite) is in an area that's somewhat in
the North or North easterly direction at about a 50 degree elevation.  This
is for the N. Hemisphere and the quality varies with the season. When
observing with a full moon, the key is to adjust your viewing position for
the darkest part of the sky irregardless where the radiant is located.  IMO
will not enter data from skies with an LM under 5.0.  This introduces too
much error for Global analysis. If  you have to raise your hand to shield
your eyes from moon effects still.  I recommend making an estimate of
blockage your hand is making and  enter  this blockage on your meteor reports
to indicate blockage.  If it's over 25%, it's adjusted.  If over...either
move or go to sleep.  If you miss a bolide from your hand in the way...that's
the breaks. 

George Zay