This is not a rules question.
I understand the RULES for illusion of calm but the spell leaves many open questions beyond the spell.
for example...
would you allow the player to manipulate the image or do they have a set non moving image, in other words... can I create an illusion of calm that looks like me cowering in a corner, or a person in a meditative pose just like every one else in the crowd or is it always simply a person standing with their arms to the side.
I know that the spell does not hide the source of ranged attacks or eliminate sounds... but I would assume that a silenced call lightning for example would simply appear from no where with no indication of the caster.
how would you rule the perception check to hear the caster if the spell is not silenced.
If I cast Illusion of calm then sat on the ground (sitting/prone) then some one attacked me... would you give them a -4 to hit, 50% chance to miss me if they hit the illusion, count the illusion as flat footed... and touch...
It says that it creates an illusion in your space... but does not mention anything about the spell ending other than disbelief or duration.. if i cast illusion of calm, then cast invisibility... can i then walk away invisible and leave the spell in place with people thinking I am still there?
In a home game I would say that the illusion is taking up almost the exact same area as you no matter if you are invisible, standing, sitting, whatever; it just doesn't make any of the hostile gestures you do. I think this is RAI. I don't see any reason why it couldn't mimic your meditative stance in this manner.
In a PFS game where RAW are king, I would say that he does stand while you lay down, and therefore you should get a miss chance when they attack it. That would be the only change.
The perception checks you asked about would have to be on a case by case basis factoring in things like stealth, other distractions in the area, distance, and maybe a few other things that didn't immediately jump in my mind.