Per the cases support page, a 240mm is the maximum you can go at the top. I'm wondering why you'd want to mount an AIO at the top when the best possible temps are found when you mount it to the front with the fans in push/pull. Same answer made here.
It's a never ending debate. I did a front mounted rad in my last build... but that was a closed front case with vents pulling air in... (NZXT S340 elite) The case had a single 140mm opening at the top so short of modifying the case I had no choice.
This time I made the case a much higher priority (Fractal Meshify 2) with a mesh front and top and room for up to 420mm.... put the 360mm rad up top blowing out with 3 140's blowing in the front and one blowing in from the bottom.
Temps are amazing... and beyond the standard 1-2C variance up or down which has been seen many times in debate testing I don't see a front mounted rad being overwhelmingly better. For me I think blowing warm air thru the rad and out the case is the best option so it went up top. I was always questioning the previous build for blowing warm air thru the rad into the case... and there's also aesthetics to think about but at the end of the day I'm much happier with this setup.
From what I've read this increases the risk of damage and lowers the life expediency of it, and further from what I've read, front mounting it may only be useful to the CPU temp and less so to the internal temp (GPU Mostly), whilst top mounting may be slightly worse cooling for the CPU and better internal temp and airflow.
I'd rather have it mounted to the top to keep internal temps better and keep it from you'know, breaking the pump.