This kept me awake too long tonight... Fusilier Angus is standing next to a fence and wants to get over it so he join the other Fusiliers playing football on the other side. The fence is 2" tall and a fraction wide, so you can't stand on it. Alguacile Cortez is sitting on a nearby roof, spying on the game. Cortez can't see any of the fence, but anything sticking up more than 3" over the ground will be seen. 1. Angus: I shall jump over the fence! By jumping up half an inch and forward 2,5" I can clear the fence and land safely with the remaining 0,5" movement. I'll simply Vault over 1,5" of the fence since my silhouette is 1,75". Cortez: What? No! You can't vault mid jump like that! You have to jump over the entire fence. Angus: But that risks me breaking my leg! 2. Angus: I shall climb over the fence! I won't have enough movement to get to ground on the other side, but I climb up 2", then flip to the other side of the fence and climb downwards 2". I'll be touching the ground and next order I'll simply finish the climb and go join the game! Cortez: Okay, that's it, I'll shoot you when you cross the top of the fence. Also, you will lose almost 2" moving over the top like that -.-;; Angus: That's just mean and I thought you just said vaulting isn't allowed like that!? Who's right in these two situations? TLDR: 1. Can you vault mid jump, if the vault ends mid-air? 2. Do you vault over to the other side of the fence when using Climb, or do you just flip to the other side without being vertical?
Coming out of retirement to say... There's no phasing your silhouette through an object. It's up and over whether you vault or climb or jump. So a 2" obstacle being moved over by a 1.5" silhouette will always result in a half inch visible above the 3" line. Now, how you address that movement when there's no base width to support it, has never really been properly addressed as far as I know. But you definitely don't get free horizontal movement while vaulting, nor free vertical movement while climbing.
Measuring Climbing on real world terrain is really baldy explained in the rules. RAW you can't. The top of the fence is unable to support the base of the Moving trooper and Climb is strictly vertical ("Climb allows only movement up or down vertical surfaces"). Practically: 2. Measure the verticals, vault the top of the fence.* 1. I'm fairly certain will open up additional weirdness. * My meta measures ground to floor and allows Troopers to vault the parapet and get the free translation from vertical back to horizontal. Ie a building with its floor 4" above the table and with a 1" parapet can be Climbed by a 4-X MOV Trooper. Climbing is already marginal enough as a strategy that penalising it more seems dull. I'm applying the same logic to your fence.
Pragmatically, I think you basically have two choices (not mutually exclusive): Ignore the thickness of fences and other obstacles that are too narrow to stand on. You can’t model underbrush that a model can actually walk though physically, and you can’t model an in-scale arbitrarily thin fence properly at scale. The fact that it’s 1/4” thick or whatever is a fabrication limitation of the model terrain piece, not what it represents. Remember the statement concerning a model’s base being fully supported during movement is a default. If you (plural) really want to deal with balancing models on 1/4” thick walls, no one can stop you (plural). After all, if you’ve got a 2” tall fence, S6 and S7 are taller than it. You probably expect them to be able to vault over the fence, even though they can’t stand on top of it. Likewise, you’re going to expect S2 troopers to walk right over 0.5” or 1” tall fencing, right?
