The lead-out burn time can be longer for shorter projects. With short projects the DVD-R will be topped up to at least 1GB with "dummy data" to avoid a compatibility issue with set top players. (Some set top players will start by moving the laser out to 30mm from the center to perform a calibration test. If they find nothing there - as they would on a DVD-R with very little data on it - they will assume an unplayable disc and fail.)
The behavior may be different with DVD+R media, as these don't need the filler data.
A different issue could be that Encore 1.5 seems to be using 1x speed on some burners. See
Is 1.5 burn slower than 1.0 ?.
