RAM tRP and why some CPUs are missing the register for it?

I’ve now heard multiple times from Buildzoid that setting the DRAM tRP latency on some CPUs to a different value than tRCD doesn’t do anything. Why would this happen? What would Intel’s rationale be to tie it to tRCD? Why does AMD allow you to set different values for it?

My DDR3 XMP timings have different tRCD and tRP values, but if what he’s saying is correct, it will default to the slowest value, so 10-11-10-30 becomes 10-11-11-30.