I wonder what causes a difference at a higher altitude...while static at rest it wouldn't make a difference, even though the pressure is less the pressure would still obviously be equal in and out, my guess is that at a lower atmospheric pressure the pressure differential of the draw has much more effect. for example at 14.7 psi at sea level with a -1.5psi draw is a 10% difference in pressure,where at 6,500 the absolute pressure is ~11.5, so the same draw is maybe 30% more draw, relatively speaking?
another factor may be that as the atmospheric pressure goes down the boiling point of a liquid will also go down, but this should cause the opposite of what you experienced, so I'm guessing that part of the equation isn't as relevant? I guess at higher altitude you might need to open up the draw somewhat on an adjustable kayfun to cause less relative pressure difference, or just draw with less negative pressure with a lite, the draw must cause a higher pressure differential at the lower atmospheric pressures of higher altitude... the pressure difference of a higher altitude itself isn't the cause, but it needs to be compensated for in the delicate balance the kayfun needs, just as a cars fuel injection, less atmospheric air pressure means less air density, and unless some fuel is cut back the mixture winds up too rich, I wonder how much air density could be a factor too? my guess is it's still mainly because the draw causes a higher pressure differential as the biggest single factor, causing more flooding at higher altitude and would need to be compensated for by effecting less pressure differential on the draw.
