Foster one BGP peer in case of AS path equality

Hi, I have an AS (204092) with two upstreams (174 and 198507). On some cases, the AS path is the same on both peers. I would like to use 198507 over 174 only in this situation (so, no localpref). If I read the documentation correctly, I have take of « Prefer routes with lower internal distance to a boundary router. ». But I don’t see where I can set this internal distance. Does anybody have any clue about that? Thanks, -- alarig