How to choose the minimum difficulty when mining in a slash pool

I’m mining on a single Ant Miner S9 with a slash pool.

There is a setting called “minimum difficulty”.

When I read their manual, Item #8 state

The pool automatically assigns difficulty levels to correspond to minor hashrates.

my Scoring hashrate and Hashrate It matches what my mine manufacturer advertises: 13.5 th/s

And my default is also set to 128.

However, even reading the manual, you will see that you need to set the minimum difficulty level to 1024 at 1/s and increase linearly with the hashrate.

According to the table, my difficulty should be 13312, which is 13 times. This is much higher than the 128 pool.

Do I need to set the minimum difficulty level?

I tried to understand the minimum difficulty, but I couldn’t find a clear and simple explanation of what this number represents.