Sorry I couldn't find the tourney in PT4, I'll give as much details as I can remember.

5€ mid-game (about 400 left / 150 paid).
Hero's stack is more or less the average stack at that point.
Effective stack for the hand = 75BB
SB has "normal" HUD stats (small sample anyway)

Hero opens KK from MP 2.5BB.
SB 3bet to 9BB
Hero 4bet to 30BB
SB calls. Pot = 62BB.

what is V's range here ?

Flop A97r

I guess it's a WAWB situation, cbet wouldn't achieve much.

SB check, I check back

Turn is a blank.
SB bets 18BB. Hero ???

I guess the standard is just a give up, we still have a 40BB stack / 50% of the average.

Is there any merit in XR all-in ?
We'd rep AK / AA, hoping villain folds AJ, maybe AQ, and of course the hands we already beat like QQ, JJ.
We block AK, so they should have a lot of those fragile hands... Assuming they call pre with those...
Assuming they fold AQ to a XR turn (I don't know about that)...

Maybe I'm just overthinking it and XR is just a classic I-can't-fold-premium-PP spew...

Thoughts ?

The hands that automatically come to mind that would 3-bet/call a 30bb 4-bet for almost half their (effective) stack are AA, KK and QQ. I think calling that 4-bet at these stack sizes with AK or less is a mistake seeing how they will likely only have one live card and are drawing to hit that card.
I think the flop check back is fine. I would call the turn bet. Most likely I would fold to any aggression on the river.
I do not like check-raising all in. In most cases you're only getting better to call you and folding out hands you may beat.

Why would those hands not just jam OOP?

Your 4bet is too big also. No reason to size this big in position and really even OOP it's too big.

Does the field think that way ?
I definitely put AK in V's range here...

I didn't even consider calling the turn cause I felt I would be committed. 28BB left in a 100BB pot (even a 128BB pot if V bets again OTR).

@killerkill : well noted about the 4bet size, I'll change that.

I don't see anyone flatting AA after you 4b for almost half the effective stack. Dont see it with AK either. This looks like, "Crap, he looks really strong here but I can't fold. Might as well call and see if I can hit or escape on a bad flop." Which suggests hands like QQ/JJ. For that reason I don't think you can give up on such a small turn bet. That looks like a cheap attempt to steal the pot by repping Ax after you checked the flop.

No way, AK is always played super fast in spots like this because "it's a drawing hand." Nobody is calling a 4b for almost half the effective stack in the hopes of flopping an Ace/King.

I'm thinking to keep possible worse hands/bluffs in.

I don't know what the field thinks. These are just my opinions and how I see this situation. To put in essentially half of your stack w AK in hopes of hitting a pair, otherwise folding to bet when you miss.... is, in my opinion a gigantic mistake. This doesn't mean that this player (or many others) don't play AK this way but again I'm just trying to think logically.

Generally you don't wanna flat when you're in the SB. So the whole idea behind flatting to keep hands in is that their range is somewhat wide and will miss flops to need to stab at. Now think about how little air or weak hands are in your 4b range. I venture the worst hand you'd have is like AJs to 4b like this and maybe KQs but those likely just flat the 3b prob anyways. So the point I'm getting at is that when there is such little disparity between villain's (you) 4b range and their stack off range to 5b there isn't value to try and trap esp when you're OOP. You'll under realize equity OOP and on flops like this (albeit somewhat rare) you'll be completely lost.

That's again from villain's perspective in SB trying to trap you IP.