We used to use ceramic tiles but found they broke too easily. One launch every one we set out got broken.
Used discs from a plow are probably the sturdiest deflectors I've seen. I've seen heavy diamond plate bent by N motors and certainly P motors. Circular discs seem to work best.
Tony
I've never thought about the thrust breaking the tiles or bending metal. But it makes perfect sense. For LPR or MPR, the tile should work great, or saw blades, pizza pans or whatever.
We use 4" x 4" ceramic tile for our LPR pads. They run about $0.20 each. I use standard tile adhesive to glue them to 3/8" or 1/2" plywood, what ever size scrap pieces I have. A 1/4" dia. ceramic tile drill to put a hole in the middle and they last at least a season or two.
They are still usable if the tile cracks, and the wood itself will hold up to BP motors for quite a while if the ceramic comes off. In fact, we used just the 1/2" plywood as a blast deflector on the LPR pads for half a season. It got pretty scorched and gouged from the A - E BP motors, but it never caught fire and it did protect the pad.