15.0 captions background

I notice that the new captions system puts a single background rectangle behind all caption text, regardless of how long the individual text lines are. It used to be the case that each line had its own background rectangle. I appreciate that some prefer it like it is now, but others don't. I don't - sometimes pacing and readability mean that one line is much shorter than the other, and a single rectangle leads to a lot of unnecessary blocked off space.

Is it possible to choose which system to use? Is there an option somewhere? I don't see anything in the EG panel.