I think the spell totems in realms (village defence missions) have inherited the engagement rule that was applied to Icarus towers. I'm not 100% certain though..
In a recent realm battle I had some fast units swarming an enemy spell totem, when I tried to move them around the spell totem it looked like the UI was indicating that any unit passing beside it would be captured in engagement..
For example, units with a movement range of 2 or 3 (which were already adjacent to the totem) could only move one hex around the totem.
It looked like the spell totem was behaving as if it had an agility stat (like an Icarus) by not allowing units to move freely around it, effectively capturing them in engagement as soon as they became adjacent.
I noticed this right at the end of the fight so I was unable to test it again on the next turn. I'll try to test it again if I get a chance to attack another village.