IPSEC site-to-site perfomance spoiled by IPS (UDP Flood), exception not working

Hi folks!

We have a site-to-site VPN via IPSec between an SG210 (600/40MBit) and an SG105 (70/25MBit) (both 9.705-3).

If I enable IPS UDP Flood Protection (SMB-)traffic through the tunnel drops to about 270 kB/s, if disable it's about good 3,5 / 2 MB/s, depending on direction.
I created an exception for the local networks and services IPSec, but that does not change anything.

The log does not show anything about UDP flood events. Any idea how to keep performance while having enabled the UDP flood protection?