Sporadic-E reflects waves in the range of 20 to 100 MHz, and sometimes higher. Theoretically it is possible to use such a phenomenon to transmit over 2300km. The speculation now is that there are two seperate phenomena that are responsible for causing Sporadic-E contacts to be possible, one that allows 1300km - 1500km and a totally seperate one for 1950km to 2200km. There is still too few examples and evidence to say for sure what causes Sporadic-E contacts to be possible.