When does a unit go "under" an entrenchment?

[J6A]

What cjsiam says is pretty much how I look at things. And, while I agree it takes time to move through and deploy, I think that's reflected in not being able to shoot until 15 minutes later.

To me, the under the counter/over the counter is "who got there first?" Whichever side starts with the entrenchment is entrenched or whichever side moves into an empty entrenchment occupies it, the other side has to take it from them.