This is an issue that seems to confuse users repetitive.
Solution: Consider ‘Realtime’ as ‘Use audio clip setting’.
That should be changed in future in the User interface, too.
If you have any proposals, place it here.
So what you need to do to use elastique for the ‘sizing applies time stretch’ feature is
to set the preferences setting to ‘realtime’ and then set elastique for the audio clip.
You can do that from the sample editor or - also for several clips at once - from the pool window.