One point that doesn't seem to have been mentioned is that you may not be able to make the position report because there is other traffic making calls on the frequency. And/or in the case particularly of HF you cannot establish communication immediately and may have to try other frequencies.
Takes me back to the days of flying through Iranian airspace in the 1970s when we sometimes had to relay a position report through 2 other a/c due to the lack of VHF cover.