just the box says where to put them in a tank and the diagram shows at either end at the top. but the holders just slide down so i though may as well just put them on the bottom asthey end up there ayway but then a lot of cable is under too
sure it is fine though as you say thought it best to check though always good to her an " yeah thats ok"
Anyway, it shouldn't be a problem as long as the filter(s) (or whatever it/they are) was/were meant for underwater use and as long as none of the water is dripping and making it's way down to the socket...
I think the reason they say to put it close to the surface is so you can provide surface agitation, if you are using a bubble wand or something of that line, I wouldn't worry about it
Sounds like the Interpet IPF's to me (cylinder shaped bodies, corner mounting)
Most internal filters are designed with submersion of part of the mains cable in mind.
Something to check is that the mains cable hasn't been chaffed from the filter sliding down the tank.