TPS does not increase even though new server nodes added

[c c]

HI,
    We are working on ignite 2.7.0. We just put entity into ignite cache
with transaction and backup(2) enabled. We can get 6000 TPS with 3 server
node. Then we test on 5 server nodes. But tps does not increase. We operate
ignite by client server node embbed in application. Except for
"publicThreadPoolSize" and "systemThreadPoolSize" other configurations left
unchanged. What problem is it ?
   thanks