In SF2, but not in PF2, a shield with the hefty trait gives standard cover.
This makes mobile bulwark (SF2) fundamentally different from the fortress shield (PF2) and opens a can of worms re. cover rules that I have not seen anywhere else.
General cover rules (identical in PF2 and SF2) state that cover is relative and that it is ultimately determined by drawing a line between your center and the center of the other creature and see what it intersects. And while the general text say "you" have cover, the examples always refer to two creatures having cover from each other.
Take Cover while Prone is an exception to the above: you get greater cover and off-guard, which translates to a net +2 vs. all ranged attacks, without needing to draw any lines (a sensible GM will disallow it if someone shoots you point blank, but that's a house rule).
Take Cover ends when you take an attack action, so no need to discuss sniping enemies after you hunker down on the floor. IRL it works very well (if you see Prone as ass on the floor but chest may be raised, while Prone -> Take Cover as belly pressed against the floor), but in game it doesn't. Striking breaks Take Cover, and you end up with a net -2 to hit and -2 to AC.
In theory, though, you could be prone, Take Cover, and then shoot a line or cone effect emanating from you. If cover was always symmetrical, enemies completely out in the open would have +4 reflex against that. Which does not make any sense.
Another exception to the rule of adjudicating cover by tracing a line between you and the enemy is the Take Cover you do with a Tower or Fortress shield, as it is generally understood (but not spelled out in the manual) to be omnidirectional like Raise a Shield.
Mobile Bulwark in SF2 says "you have standard cover."
Does it mean that enemies you Strike are at +2 AC, and that if you Trip someone they have +2 reflex? If yes (by logic of having a massive shield in the way), why is there no penalty to grappling an enemy?
The Solarian's Eclipse Strike has the same issue. It says that YOUR cover increases from lesser to standard to greater. Does it mean the cover the enemy gets from you too?
You Eclipse Strike someone from behind a wall vs. AC+2, and gain Greater Cover from them for a sweet +4 AC and +4 reflex for as long as any of that cover lasts. Or, even better, you Eclipse Strike at no penalty and then you Stride behind a cover. My (arguable?) reading is that Eclipse Strike applies to all cover for a round, not the cover you already have.
But if you Strike again (say a Nimbus Surge), do they get +4 AC?
And of course there's the combo Mobile Bulwark + Eclipse Strike vs. someone larger than you.
Eclipse Strike, raise Shield. Your standard cover is immediately upgraded to greater against that enemy. But then you Strike again (e.g. nimbus surge). Did you just shaft yourself and you now have to hit at -4?
There is wording for GM fiat: https://2e.aonsrd.com/rules/422-special-circumstances
> Your GM might allow you to overcome your target's cover in some situations. If you're right next to a narrow window, you can shoot without penalty, but you have greater cover against someone shooting back at you from far away. Your GM might let you reduce or negate cover by leaning around a corner to shoot or the like. This usually takes an action to set up, and the GM might measure cover from an edge or corner of your space instead of your center.
Examples of asymmetry are found frequently in the wording for Concealed. a dazzled creature treats everyone as concealed, but not the other way around, if you have blur everyone treats you as concealed but not the other way around, and many effects like Obscuring Mist explicitly state that "All creatures within the mist become concealed, and all creatures outside the mist become concealed to creatures within it." The Solarian feat Nimbus Rush is another explicit case of asymmetry in giving the Concealed condition.
To recap:
- Prone -> Take Cover -> Lightning Bolt against an enemy in the open: it is patently absurd that an enemy should get +4 reflex bonus
- Concealed is asymmetric by default and the manuals explicitly spell out when it is symmetric
- Raise mobile bulwark -> Strike or trip: do they get +2 AC and reflex vs. you? Does the "shooting from a slit" rule apply?