It is my understanding that the IPS modules analyze packets permitted to traverse through the host ASA. If your ASA ACL only allows TCP 80 and 443, then it might not look like a sweep to the IPS module's rule. The SSM IPS does not see that which is stopped by the ASA.
Now, if you built a server, placed it in a new/separate (no access from outside) DMZ and permitted an inside host ip any any and then ran a sweep, see if it fires then.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...