How Exactly Does Blessed Boundary Work? Is the Goblin, Kobold, or Orc Correct?

[Balkoth]

The spell in question, Blessed Boundary.

Basically a burst in 5 foot increments, boundary is two inches thick, attacking through the boundary gives cover, trying to cross or stand on the boundary has a chance to deal damage and forcibly move you.

A goblin, kobold, and orc cleric each cast Blessed Boundary.

"Hah!" says the goblin. "Anyone attacking me will have to attack through cover, I am protected, even if enemies don't have have to make any saves to attack me from 5 feet away."

"Nonsense," says the kobold. "You want to move the boundary further out so enemies have to try to pass through it, if they fail their save they're kicked out and have to try again. This is better than having cover from all attacks, even if it means someone who makes the save is safe and sound in the barrier with you and you don't get cover."

"Amateurs," says the orc. "I get the best of both worlds. Anyone attacking me has to deal with cover, plus every square within 5 feet of me forces the saving throw to not get punted away. And even if they make their save once, they have to keep making a save each turn to not get pushed away."

So which clerics have valid interpretations of Blessed Boundary in this case? Where exactly is the two inch boundary and what squares does it impact?

[Squiggit]

None of them, bursts are created from a corner, but all your examples are drawn from the center of the square.

Here's an area reference for burst shapes.

[Balkoth]

So a 5 foot burst has four safe squares to stand in? Do the squares directly bordering the 5 foot burst force a save for creatures standing in them, or is the boundary between squares?

[Errenor]

None of these are right as a burst is always coming from a corner of a square. So the minimum is 4 squares (5 ft burst) and count from there.

Balkoth wrote:

So a 5 foot burst has four safe squares to stand in? Do the squares directly bordering the 5 foot burst force a save for creatures standing in them, or is the boundary between squares?

Yes. No, the boundary is between. 'End of the turn' only matters for creatures which take more than 1 square.

[Trip.H]

blessed boundary body text wrote:

Manifestations of divine force appear in the hundreds, swirling in a massive, protective sphere. These typically look like spiky fragments, but often take on an appearance themed to the deity of the caster. The sphere is hollow, with the manifestations forming a shell 2 inches deep on the outer edge. You can choose to make the burst smaller, in 5-foot increments, when you cast it.

The shell provides cover and can intersect solid terrain without affecting it. The shell deals 7d8 force damage to each creature who intersects with the shell when the sphere's created, or who attempts to move through the shell. The creature also takes the damage at the end of its turn, but only if it didn't already take damage from the shell that turn. The effects are determined by a creature's Reflex save.

There is no text to indicate reaching through the barrier has any affect. So melee attacks crossing the boundary are not affected by it's damage nor move disruption. Only the cover aspect would be in effect.

In order for the spell to function, we will need an abstraction for squares, where the spell itself is not spherical, and zigzags perfectly along square borders.
The orc's version is impossible for that reason.
The difference btwn a burst and an emanation has already been covered by others, which is why the goblin's is impossible.

The orc and kobold both have the right idea, so long as they can damage targets at a distance, it usually will be a better idea to force a crossing and leave the cover benefit as a help against ranged attackers.
The goblin has ensured they will have cover to all others, but those others will have cover from the goblin as well. That bubble also ensures that only the goblin will be harmed by crossing the barrier, especially ironic as a Shove upon them would only damage the goblin.

However, it's notable that none of the clerics have allies, as the spell is not friend-safe. This means that most of the time, it is best to use this spell to bubble the foe formation turn one, as it will otherwise be a serious hazard to one's own team. Even the cover is fully mutual.

The spell best placed to circle an area the party does not plan to move into, and one that foes will need to move out of.