The following may be of interest to those enrolled in more than one project:
It is being posted because a close match wasn't being shown for one participant (KitB in the example below), the reason being that he had enrolled in another project, and that was the one selected (his secondary project) on his matches page.
Even though he had "match against entire database" selected, his closest match, which was with someone enrolled in his primary project, was not being shown.
The matching person (Kit A in the example below) had his preferences set to match only with that project, which, according to the explanation below from FT DNA, is not going to show up on Kit B's matches until Kit B's project is changed to the same project.
If kit A has his preferences set to be compared against his surname projects only, he will only be compared against participants who are in that project AND have that project selected on their personal page (if they are in more than one project). If kit B has his options set to be compared against the entire database, his results will be compared against everyone else that also has their preferences set to be compared against the entire database AND those who are in the project that is selected on his page at the time.
From this, it could be deduced that it is therefore best to set your preferences to match against the entire database, and make sure that you have your main project selected when you check your matches.