DDR4 main timings is CAS, tRCD/TRP (usually set to the same value) and tRAS.
According to Raja @ Asus, to improve stability,
set tRAS equal to CAS + tRCD + tRTP (minimum value for tRAS). So in other words, tRTP should be equal to tRAS - TRCD - Cas.
Then set tWR = 2x (double) tRTP.
tRTP should never be less than 5.
said this also.