Wasn't Grealish right next to whoever headed it? I can't really remember and tbh as said below I'm just not shocked when those are given however harsh it looks. Shaw one was basically watching a corner come in from 15 yards away and under no physical pressure from anyone else just decides to lift his hand which was just a bizarre action considering he'd have a very good game but loads of defenders lose their bearings like that, Lewis Dunk had done the exact same thing in the game Brighton played after the cup SF at Forest.
I assume distance and pace of shot is still taken into account.
About as close as Eriksen was today (and closer than Romero was when proximity was claimed to be the reason why it wasn't given). But like I said, arm above head is specifically mentioned as "rarely natural" in terms of body position. You can also see from the images posted that in the short time that the ball travels from the header the arm goes from shoulder-height to above head height, so there's a movement towards the ball too.
For me, the Grealish pen is a stonewall pen under the current guidelines (arm above head). You can argue about the guidelines being dumb, but they're in place and in that context it's an obvious pen. But it's telling that in the collective consciousness (you're not the only one), it's seen as a controversial call whereas another pen that's just as obvious for the same reason according to the guidelines (arm above head) is totally the right decision according to everyone.
And now we're seeing it again with all the pundits claiming that the Romero one is not a penalty due to proximity, and then in the same breath you get people (at least on Swedish TV) saying that the Eriksen one is the correct decision despite the proximity factor and the arm not being elevated above head height. You can even see Kim behind Eriksen with his arm in a similar position as he's running/turning towards the ball. What are the odds that two players in the same image would simultaneously take up unnatural arm positions? Could it actually be that the arm is "justifiable by, the player’s body movement for that specific situation" (using the rule book's wording here)? And if it could be seen as a justifiable position, what actual criterion has been fulfilled to intervene tonight and give a penalty against Eriksen? It's not deliberate with a hand movement towards the ball as it comes at him, the body hasn't been made unnaturally bigger, and it's not in a position above the head which is rarely seen as natural. So what exactly has prompted the VAR to get in there and recommend a reversal of the on-field call?