So putting together the info that one square is burned, with the map and text above from Quill’s IC post, I think what we have is the following happening at each slit and the squares around them, which is most of what Blisss is passing along in greater detail than what I wrote.
The enemy nearest the wall who retreated is the one at the top, with the Shredstorm at the topmost slit in front of the creature. That’s the slit on the party’s right, from their perspective. However, according to the map that enemy is not the one where Flintspark is in the web, so that enemy must have seen the flame and smoke from the other slit and decided to back up before the fire spread to the slit in front of him.
The square with no illusion or web, where the party can see the wall, is the one where Flintspark is, the lowest slit. It’s the one nearest to Blisss, who should be able to see the flaming web directly, looking through the slit. That square is to the party’s left, from their perspective. They may now be able to see the enemy creature directly behind that slit, so if Adhuil can get a shot past Flintspark he could theoretically send a holomancer attack through the slit at the enemy creature. If Adhuil moves up close and into position, he may be able to see around Flintspark to the slit. At the same time Adhuil could try to make sure he’s in range of the spell Blisss will cast.
The square with the damaged wall is the one in front of Loptr, which is also where the center slit is. The horrible-headed creature is directly behind that slit. Blisss may be able to see the cracks, dust, and beginnings of rubble, as well as hear the sound of Loptr’s strike, so he may know where Loptr hit. Blisss might have line of sight to where Loptr’s left side is, at an angle through the slit nearest to Blisss.
On El’s turn, the Shredstorm may be able to stretch itself out to cover the enemy’s square. If not, another option for Adhuil on his turn is to burn away the web holding the Shredstorm so it can launch itself against the enemies on the other side of the wall. Adhuil knows where the Shredstorm went into the illusion, and – if it’s really right at the slit – may be able to get confirmation from Blisss based on what Blisss can actually see.