Rush export file size

About Rush 1.5.16 :

In Adobe Rush I have selected 5 MP4 video files (in 720 P) with these file size : 43.4 Mo, 15 Mo, 64.9 Mo, 13.1 Mo, 16.8 Mo. The total for all the videos is of 153 Mo.

If I put all these videos inside the timeline of Adobe Rush, and if I go on the "Export tab", in "Automatic mode (720 P)", I have an export file size of 811 Mo (instead of 153 Mo for the original file size) !

Why this huge difference of file size ? Even if I select low quality I have a huge difference.

Could you make Adobe Rush make an export file size near to the  original file size (for a lossless quality export) ?