i also had very high rejections on coinsolver.
i resolved this with a diff of 256  (password set as d=256) . i used coinsolver.com:5555

and for 24 hours , i got only 11% rejection , i tested with 3 fury , and they all give me the same percentage.
it is a huge improvement  as i was having 25% two days ago with a diff of 512 , i also tried with vardiff without success

hope it helps