Here is where the DX cluster can be very helpful--it helps to make sure you aren't calling on top of another DX-pedition! Make sure there isn't a big DX operation up 5 if you are going to blindly call there! Of course, accidents do happen, not much you can do if a rare DX station shows up 1 kHz below another!
Doesn't the DXpedition have any responsibility at all to make sure the frequency is clear and another DXpedition isn't already transmitting where he will be asking stations to call? That's why I don't understand why they list their transmit frequencies months in advance. The expedition does not have anymore right to those frequencies than anybody else, but naturally one station should move for an expedition. If it is a net who has been on the frequency for a long time good luck on getting them to QSY since most feel they own the frequency.
If two DXpeditions are that close one of them didn't checkout the band ahead of time and most of the expeditions now have some kind of internet service even in places you'd think not. If they don't have access to a spotting network there is an old-fashioned thing called listening to the band before transmitting.
An expedition should not be excused from the normal courtesies just because they are in some remote location.
BTW, I don't think I ever wrote that one should call blindly w/o checking out the frequency but if a DXpedition is transmitting on, say, 28.490 and asking for stations to call 5 to 10 up good luck in getting 1,000 stations to QSY if another expedition is there.
When I wrote sometimes a modest station should exceed the split range I was talking about a few hundred cycles, not 5 Mhz!