It's hard to say what the "norm" will end up being.
I think it may have something to do with the number of cast members that staff the entrances at any given attraction and whether or not the standby/FASTPASS entrances are next to each other. At a ride like Tower of Terror, there are usually three cast members at the entrance because the standby/FASTPASS return lines are right next to each other and Disney staffs both. There is usually a third cast member hanging out as well. Same with Soarin' where standby and FASTPASS return are side by side. At an attraction like Splash Mountain, the FASTPASS return line is a considerable distance away from the standby line. So if the FASTPASS cast member at Splash Mountain is having an "issue," there is no one else to take over looking at other people's FASTPASSes. The same is true at Space Mountain where the FASTPASS return entrance is off to the right from the standby entrance and cast members wouldn't be able to easily take over if there's a problem with one person in the line.
That seems like the most reasonable explanation for why we would be seeing longer lines at some attractions and not others.
I think it may have something to do with the number of cast members that staff the entrances at any given attraction and whether or not the standby/FASTPASS entrances are next to each other. At a ride like Tower of Terror, there are usually three cast members at the entrance because the standby/FASTPASS return lines are right next to each other and Disney staffs both. There is usually a third cast member hanging out as well. Same with Soarin' where standby and FASTPASS return are side by side. At an attraction like Splash Mountain, the FASTPASS return line is a considerable distance away from the standby line. So if the FASTPASS cast member at Splash Mountain is having an "issue," there is no one else to take over looking at other people's FASTPASSes. The same is true at Space Mountain where the FASTPASS return entrance is off to the right from the standby entrance and cast members wouldn't be able to easily take over if there's a problem with one person in the line.
That seems like the most reasonable explanation for why we would be seeing longer lines at some attractions and not others.