It actually works even if your centrifuge is faster than the sluice. The centrifuge can insta-pull an ore in to process (it doesn’t occupy the visible inventory slot) and your tiny ores will still proceed to the right. Essentially the pipe is trying to output everything in the same tick. The first inventory slot goes to the centrifuge and the remaining 7 slots go to the adjacent pipe, preventing a double deposit.
If you use anything other than an 8 slot pipe you will pull a tiny purified like 1 in 50 which bottlenecks the whole thing.