For example, why do altocumulus clouds fail to form at 6400m in high latitude locations, but will form at this height at a lower latitude? Is it simply an issue of temperature?
It depends on the height of the troposphere. On the equator troposphere has at least 12 km height, but in the polar latitudes it might be even less than 8 km. That difference in troposphere altitude allows clouds to form differently depending on the latitude. The second reason is that higher parts of the troposphere closer to the equator are warmer and contain more moisture than in the polar region.