Wow, now I'm really confused. Some people say 8.5 up to 9.5, and now I get one at 7.5.
Is there a manual online where Royal Exclusiv lists the optimum sump depth?
The Alpha's are in that 9" - 9.5" range, not the SM's. The SM's can be ran that deep, but I think you'd be better off around 8". HTH!