Multiple update : Activities priority - Right Management question

Hi,
I have a question about the right management of fields for activities in 'multiple update' form.
As an admin, in multiple update form I can see all the fields available (especially priorité) But as a project Leader, 'priorité' field is not available, 
I have check the defaults rights : no clue as project leader have default access to priority modification on an activity of his project. I have not seen any forms or screens to specify the rights on 'multiple update' screen.
How can I give access to multiple update on activity priorité to project leader ?
Thanks

 

Thanks for your answer.
I confirm that the defautl value seems good :
multiple update : yes
Change priority : yes
Change priority others element : yes
in Fact, the default profile of our project leader are members (so they won't move around the projects on the root in planning mode ) and as such the list is calculed according to this profile and not the profile of the project.