A general helper and explanation on wave attacks
The general idea with waving is that the first of your attacks to hit should not defeat the defenders on it's own; it should produce an inconclusive result so that there's another round of combat. Then your succeeding waves hit in the 20min of that first round; they have no effect when they hit but will be added to your forces for the second round of combat.
It's just a matter of timing attacks carefully, and being sure you don't inadvertently bash - some cunning defenders might send their troops away at the last minute so that what was supposed to be a ten-pillage-wave attack becomes just a a ten pillage bash fest. If you're sending enough waves that they might end up bashing if the defenders leave, be sure to have spies there first!
The basic outline for a wave attack is:
1. Place spies (if you're sending enough attacks to potentially bash)
2. Ensure moderate size force hits first, generating a second round of combat
3. Make sure there is a second round of combat!
3. Second big overwhelming crushing force arrives 5ish minutes later (gives you time to change plans/withdraw if something goes wrong with the first attack)
4. Check combat reports and re-spy garrison if necessary!
5. Subsequent waves arrive 5 or so minute after huge overwhelming crushing force but within twenty minutes of the initial force(again, gives you time to change plans if needed)
