The file sizes were all around 2000, which I guess is about right for 2 seconds of video:
I then changed the pre-event recording to "0" and that seemed to fix it.
Now my issue is that it seems to be recording for 100 seconds even if the trigger event moves out of the frame within 5 seconds. I was hoping it would be more dynamic than that, but perhaps I should lower the max recording limit to 30 seconds, to save sdcard space. I just worry about missing any movement that is actually longer than 30 seconds if I do that.