Sony XAVC S best render setting

bluerum66

Hello, When i import a 1080P XAVC S file to sony vegas I check file properties and it says its 4GB for 11 minute file. data rate is 50014kbs which i understand means 50 mega bytes a second. When I render the file in vegas I use a custom template  for project properties 1920 by 1080 field order progressive scan pixel aspect square frame rate double pal deinterlace none. I then render as 1920 1080  50P. I check custom settings the bit rate setting is set to its highest 25,999,360. When i render the file the size of it is 1.67GB.  data rate as now dropped to 21374. I seem to have lost a lot of data from the original file. Is this normal or do I need a newer version of vegas to render it at  50 mega bytes a second and keep the original quality. Its gone from 4GB to 1.67GB. I have sony vegas platinum 11.