We get 4 or 5 shells on a busy day, but its not just at dodore, everyone ports around to try an make the most of their time while leaving a mule at dodore for weather.
People will never 'take turns' at claiming, and they shouldn't have to. if one mob is being fought, then there should be alternatives to go to. With smaller groups, even if there are alternatives, there will be the same number of groups at each NM, rather than 1-2 at one and 1-2 at another. With multiple groups you will end out with more people standing around doing nothing which will just frustrate people.