When does a unit go "under" an entrenchment?

[cjsiam]

I guess we have to remember that this is a 15min time segment.....
That an infantry in combat movement moves 3 hexes in 15min......so that "movement" into the entrenchment hex could be the 1st, 2nd or 3rd of the 3 movement points expended over that 15 min.

It doesn't take a lot of time to jump into an entrenchment...

Picture the scenario where an enemy unit is adjacent to the entrenchment that the unit is about to enter....he's going to be firing at the unit as they try to get in,
but they will be in the entrenchment pretty quickly as well.....

moving into a woods they take advantage of the terrain immediately (and looking at maps -- which is always suspect---that might be the 1/3rd of the hex on the other side, but still they get the modifier.....

So providing the modifier for the 15min period makes some sense to me...and seems consistent with how the rules work....I would hate to have to modify the mechanic
based on which of the 3 movement points....or part of movement it happened within....

We have to recall this is an aggregation of activity over 15min....at 200 yards(or more)
....clearly they are vulnerable for a short period as they move into the entrenchment
but I'd think that lasts no longer then it does as they move into a partial woods hex......so....I'd think the entrenchment applies.....at best--the firing unit gets
to fire with the -1 opportunity fire---but I think that might also be questioned....but....on that I'd go either way....

The RAW seem to say they get the entrenchment....as it's the terrain hex they are in, and they are considered in it on entering.....