Bonjour Jean-Marc 🙂
You need first to assess the number of Pagings in the LAC,
and the number of Location Updates in each cell of this LAC.
If the nb of pagings is above the threshold defined by your manager, then you should reduce the number of cells within this LAC
If one cell is having too many LU (= inducing SDCCH Assignment Congestion Rate too high), then you should try to define a better border of LAC. If a highway is crossing the border, you will have too many LU in the 2 border cells. It could be smart to avoid crossing highways (if possible)