The only way to solve this problem is to go to cell level what you need to do is:
1- Check the LA and if the cells are properly homed to the destinated BSC-MSC
2- Check the cells @ LA borders
3- Check if there are any cells shooting from far away to this LA
4- Set some plans to downtilt shooting cells
5- Study the possibility to re-plan the LA
6- The most important issue is to check if there is a best server because you may have cells are doing a cell selection/reselection due to no best server thus doing a high LAU.
Hope you’ll get rid of your problem…