[Barry_R]

Cylinder pressure forces rings down against the groove, and out toward the cylinder walls. Light throttle or backing off the throttle will reduce pressure to the point where inertia and inter-ring pressures take over and the top rings are not pushed down & out.

The downstroke flow of some residual combustion gasses through a gap help to move scraped oil toward the piston's drainbacks and the sump. Lacking any downward impetus, the oil will cause the second ring to eventually hydroplane and the oil can contaminate the combustion chamber.