I can feel your frustration.
I would attempt to remove all of the top coating off, and go back to trying to remove the actual tiles again. anything else is really going to ruin the overall look of the tank, unless you can completly cover it up, but it would always be in the back of my mind. You just need to get one up, then the rest will be easy with a metal paint scraper.
You obviously did every thing you could to rip them up befor you moved on to something else, but the tiles will break befor that bottom glass will. The bottom glass is 1/2" while that tile is 1/4" or less.
Heres what i would do...... I have cut tiles to fit my tank befor, i used a handheld glass cutter to cut them. Its really easy to use, you basically score the area you want cut and then snap the piece, it will break along the point you score. If you were to score the cr@p out of a tile first, in the middle of it, this will weaken the tile and snap it up easyier. I would also have some silicone solvent on hand, the type of stuff that disolves the silicone, put it in a plastic syringe and try to get it under the tile, adding more solvent as you work further under a tile.
To get the top coat off, acetone should do the trick.....
worse case scenario, you'll have to reseal the tank from the silicone solvent, but no big deal. If your carefull with it, you wont need to. you just need to get one tile up. One of those tiles isnt as siliconed as the rest, you just have to find the weakest one.
Next time just lay the tiles in, no need to silicone them down, theres no need for it. They'll stay in place on there own.
Good luck, hope that helps.