Ethermine vs Flexpool

Hi

I test some pools and try to do my own opinion with
nanopool
hiveon
flexpool
ethermine

What I noticed is with ethermine is that I have much more stale share than with any others. Any may know what is the cause of this ?
I have no connection problem nor high latency ( 7 ms )

My apologies for asking a question related to your question:

All other things equal is pool hash rate/competition a variable in “stale shares”?

In general: When comparing hash the largest pool(14x) in your list to the mids(4x) and the small(1x), should we expect the larger pools to move on to the next block more frequently than the small ones?

Or is my understanding of a variable in “stale shares” as submitted/arrived/late incorrect?