Six meter openings are sparse when compared to HF because 50Mhz is on the "edge" of what the ionospheres E and F-layers can refract on a regular basis. It takes exceptional solar activity found during the peak of a productive 11 year cycle to propagate six meter signals via the F-layer - the peak of cycle 19 in 1958 was one such time that has never been duplicated - regular six meter, round-the-world openings were happening almost daily!

On the other hand, E-layer propagation via six meters happens regularly, but it is seasonal. Most of the sporadic-E ( Es ) propagation centers on mid-summer due in part to more direct solar radiation. Solar particle storms and X-ray flares can cause a jump in E-layer ionization causing a highly energized E-layer during the seasonal peaks at the spring and fall equinox.

Sporadic-E is said to form as highly dense, ionosphere patches, a few hundred miles wide, at  E-layer heights. These patches are said to drift at high speeds.

Geometrically, the E-layer is lower in height than the F-layer so one single hop propagates to a maximum of about 1200 miles. This can be extended to 2400 miles when two Es "clouds" are in just the right place. Six meters is also affected by Troposphere ducting, but I'm not familiar with the statistics.

Off season Six meter DX...

Keep in mind that although very high solar activity is needed to regularly allow the F-layer to become dense enough to propagate six meter Dx signals, this kind of long-haul propagation can still happen sporadically when solar activity is not at maximum. It happens by the use of more than one propagation mode.

An example of this is when our six meter signals experience Es skip here in W2, reaching 1200 miles to the southern U.S., then bouncing into what's called the equatorial anomaly, where just above the magnetic equator, there is a highly dense "bulge" in the ionospheres F-layer that allows the signal to propagate over the equator into south America. The signal may then encounter E-layer skip again to propagate even farther. This can also happen on a S/W direction towards the Pacific Islands.

By the way, the equatorial anomaly is also responsible for enhanced trans-equatorial HF paths, and is especially noticeable on 10 and 12 meters. You've probably tuned across 10 meters and noticed that even when all other paths are shot, you still tend to hear LU's ( Argentina ), YV's ( Venezuela ), PY's ( Brazil ) etc. It's enhancement is also responsible for higher MUF's (maximum usable frequencies ) to HF paths like New York-to-New Zealand.

There's also six meter meteor-scatter that can be worked on a regular almost daily basis, and occasionally six meter Auroral propagation, but I'll leave that for another time.

In a nutshell, I'd have to say that patients is key with six meters, regardless of what propagation mode your expecting. Noise is what you'll hear most of the time, but when the band opens, all hell breaks loose and stations come out of the woodwork!