When you are on the Bitbucket PR page you and have the menu collapsed you don't have any possibility to see on which project you are currently reviewing. 

When hovering the repository icon (yellow arrow) a tooltip with the repository name is displayed. 
Maybe on this the project name could be added as well. Since it's it's expanded below repository name the project name is displayed 

Reason: When you have code review page open and it's configured to side by side view you need to collapse menu cause you need the space to see the code