I just did a quick test on the 3rd floor of my freighter, just to make sure I could place everything without issues caused by whatever is placed a floor down. I noticed that I could not place small hydro trays on the floor directly above my already existing farm room. Something from below was interfering. I also noticed that some room parts could not be placed because of lights I had placed a floor below.
Anyways, I can confirm the coloured lights not being lit when placed on the edges of hallways, just like you show:
Interesting how the light that did not work, now remained when a room was attached. This light all of a sudden found power, although floating in the now doorway.
Placing small hydro trays appears to work for me. I tried all 3 varieties of rooms attached to the X-hallway.
Maybe something to do with the default floor when it comes to small hydro trays?
I can’t really test default floor on freighter, as my default floor is fully altered and filled in (Next save). I will see if I can find spots where the trays do not power.
I just checked my farming room (default floor) to notice all small trays having power. Most of the large trays are receiving power as well, although some remain unpowered. There appears to be some pattern to it, but have not quite figured it out.
I tried placing small trays as 2x2 (equal to large tray), but noticed only 2 can be placed in said square. It does not appear to matter how you place them, but always only 2 allowed within the 2x2 area. Really odd.
I am unable so far to find a spot where a small tray will not power along a wall on its own, like you have @sheralmyst
Another fun fact, aiming at power input on trays in build mode, gives the wire menu. No attachment can be made however and a notification says ‘out of range from base’.