1. You should fix this problem with deauth and extensive data lost...
2. You should have option that logged user from pppoe or vpn can have 2 different speeds to 2 different domains (2 queues) with single public ip address:
User who is logged to pppoe concentrator (which is mikrotik internet router) and have one public ip address have
1. for example: 512k (of speed) to internet
2. for example: 1024k to local network between other users in this pppoe internet router
at the same time. You should be able to set this 2 (first and second to be variuous) speeds from radius software..