Hi rodolphe,
The placing of your member cards in the search results depend mainly on the primary sort parameter and it has 3 option: Last Active, Newest Registered, Alphabetical.
Although, you might be interested in using a third party plugin to create a “Featured members” tab in your directory, thus pushing forward a handpicked selection of members.
BuddyPress Featured Members (https://wordpress.org/plugins/bp-featured-members/) is free and partially supported by Gwangi. You can give it a try and see if that solve your issue.
Best regards,