http://yugioh-wiki.net/index.php?%A5%C0%A5%E1%A1%BC%A5%B8%A5%B9%A5%C6%A5%C3%A5%D7#v68ee46e
When this card is sent to grave/destroyed
These types of trigger effects can be activated in damage step.

http://yugioh-wiki.net/index.php?%A5%C0%A5%E1%A1%BC%A5%B8%B7%D7%BB%BB%BB%FE
These effects can be activated in PHASE_DAMAGE_CAL.
So these types of trigger effects should be allowed in damage step as default.
Otherwise, we'll need to add EFFECT_FLAG_DAMAGE_STEP and EFFECT_FLAG_DAMAGE_CAL in all EVENT_TO_GRAVE effects one by one.