Had this come up in a game yesterday

If you play with the 'Unprepared' deployment zone (red 5 deep, blue 1 deep) it's legal to place terrain very close to the blue deployment zone (it cannot touch it but it can be just over range 1 away from the table edge

Terrain cannot be placed at range 1–2 of the edge of
the play area, at range 1–2 of other terrain, or touching either deployment area.

If I have a unit that is 2+ ranks deep, it cannot fit into the range 1 deployment zone, so by rule 26.2, it must be deployed so that it's back edge is touching the edge of the play area. It's entirely possible to deploy this unit so that it overlaps any terrain that is placed very close to the deployment zone (try deploying the forest just over range 1 from the table edge then try and deploy 'behind' it with a rank 2+ unit, it overlaps the terrain.

My question: is it legal to deploy overlapping the terrain in this manner?

Strict reading of the rules as written, you can do this, further reading does get a bit odd though, my initial thought would be that as soon as said unit moved, if it was still overlapping the terrain after it's move, it would enter the terrain, however:

81.1 If a piece of terrain has a capacity value, a unit can choose
to enter and occupy a piece of that terrain when that unit
collides with it.

18 Collision
After a unit performs a march (?) or shift (?) action, if it is
touching an obstacle that it was not touching before performing
that action, it has collided with that obstacle.

The collision rules are written such that if I was already touching the terrain, I am unable to 'collide' with it unless I first move away and then move back in again. This is mostly because apart from the deployment scenario above, it's not possible to be overlapping a piece of terrain, which does kind of imply that you can't deploy overlapping the terrain at all.

This happened in a game yesterday, in the end I deployed slightly to the left of said terrain and used a shift to move into it on the first turn, but it would be good to get an official clarification on whether you can deploy overlapping terrain or not. I think it's only a problem in unprepared. I guess it might be a problem with huge units in hammer and anvil or battle lines but I've not checked the relative sizes of trays to see if that would be an issue

I would say you can't deploy overlapping the terrain, so setting up near it then shifting into it like you did would be the right move.

It seems the likely answer, but there is nothing preventing it in the rules as they are written that I can find. At this point there is no solid argument for preventing someone from doing so if they wanted to try.

Even if the deployment zone is 1 deep the terrain still can't be set up within range 1-2 of the edge.

I don't have my stuff with me but how deep is 3 connected trays in terms of the range template?

33 minutes ago, stet2 said:

Even if the deployment zone is 1 deep the terrain still can't be set up within range 1-2 of the edge.

I don't have my stuff with me but how deep is 3 connected trays in terms of the range template?

The trays and ranges are the same length but range 1 has a little extra, so about range 2.5.

22 minutes ago, stet2 said:

Even if the deployment zone is 1 deep the terrain still can't be set up within range 1-2 of the edge.

I don't have my stuff with me but how deep is 3 connected trays in terms of the range template?

The first point is super valid! Shame on me for working off the assumption of 'edges' being the two sides and not including the player edges, having it further away from the player edge gives you much more deployment space to work with.

3 trays comes to just over the half way point of the 3 band on the ruler, so even though this gives you more room to deploy, it's still potentially an issue for the largest units.

At present this situation can only occur in certain situations. Normally only a 3x3 or greater sized unit would be able to physically overlap terrain placed just outside range 2 of the edge and would be prevented from doing so as the max capacity of any terrain so far is 6 trays.

However, if the deployment area was only 1 deep such that a 3x2 unit (oathsworn cavalry for example) cannot fit in even when placed sideways; then placing them with their rear to the board edge would allow them to overlap terrain placed just outside range 2 yet still be small enough to occupy the terrain.

I'd probably rule that they can't deploy touching the terrain (at least until an official FAQ answer on this point) as this seems to be the intent of the rules regarding terrain deployment.