If you look at the mapped HF contacts on my PE4KH Amateur radio site you might notice the contacts made in the 20 meter band normally have a ring around my home location, unlike the contacts in the 40 meter band. This is caused by the 'skip zone', explained much better in the Skip zone article on wikipedia complete with graphs of how the radio waves travel. The size of the skip zone depends on the frequency. It is usually absent in the 40 meter band. In the 20 meter band it normally makes it hard to make contacts with the rest of the Netherlands, Belgium, England and Germany. Today I had some 20 meter PSK63 contacts with nearby stations in the JO01 maidenhead locator square. This is 'too close' for normal 20 meter contacts via skywave (radiowaves reflected via the ionosphere) and 'too far' for groundwave (radiowaves travelling directly). But with all the interesting conditions on other bands happening the last weeks this is probably also a case of some interesting type of propagation.