I say if you are not overlapped when you enter the 3 boat length then you do not have to give room for the boat behind you to round the mark. Some things were said above that are not correct. It is when the first boat enters the 3 boat length zone that the presence of overlap is determined (18.2b). Also, you do not have to stay clear of the boat behind you when tacking as you would normally have to do (18.5b). But be careful, if you are starting your tack as you enter the 3 boat length zone, you might create an overlap. The other boat is overlapped with you if she is forward of a line abeam of your stern. That line moves a lot when you change course so it really depends on the details of your heading when you hit the 3 boat length zone.
The rule book is 153 pages long. I copied the sections on when boats meet and the important definitions and it takes up about 5 pages. Those 5 pages answer most of these kind of questions.
When boats meet.