Do not overlook Gary second point.

Remaining duration start depend on the out-of-sequence setting. There are several settings; such as progress override and retained logic among the most common, P6 I understand provides another and recently I learned of a % rule. All applied across the board, none a sure bet. I agree with the recommended practice of using retained logic but will add always correct logic even when your choice seems like in agreement, if latter on you change options it will no longer be in agreement, on a claim the faulty logic might be questioned as well as any late fix.

Take a look at the following image.

If you setup EF to be day 26 the Overridden  option will calculate RD=18 days. The second option will calculate and change RD to 6 days without any warning if you fix EF.

Under resource leveling this is somewhat more complicated and P6 introduced what they call Remaining Float dependent on resource availability but not necessarily equal to resource constrained float judging from unreliable float computations by P6 observed by many as reported in several Planning Planet threads.

Ron Winter provided us with an excellent reference for P6 Dates you shall take a look. A reference I never get tired of posting as I find it so good.

http://www.ronwinterconsulting.com/Understanding_P6_Dates.pdf