Someone will know how to maintain a fixed stratum difficulty in the pool, rises dramatically preventing receiving "accepted actions"?
or is it natural?
IMHO auto is the best;
If you talk about getting smammed with low diff. shares at start - set start diff. higher
If you talk about miner diff. going too high and got disconnected - set diff. change step to smaller percentage
By default (what makes sense) miner is auto adjusted to put shares_count/time_period whatever his hashing power is.