Ahh I see.
There are many ways reduce latency, a frame cap is fundamentally a delay in frame drawn before being rendered by the GPU.
RTSS is way better at limiting FPS because its less erratic, the reduced latency you see from NVCP or in game is because its erratic.
What you see in game latency stats is possibly an averaging method, so you can have random highs and low in latency but on average its better but not consistent.
Nvidia low latency mode will only reduce latency when GPU bound, but will add latency when not GPU bound.
I prefer using Reflex On rather than +boost because the frametimes are less erratic.
Check your GPU usage, if it remains below 95% underload in Val then you should not hit GPU limit.
Another thing to try is giving priority to RTSS itself, set a high priority to the RTSS.exe. (DO NOT give priority to the RTSS hooks loader)
Remember that frametime latency will increase as you reduce FPS.
1/60fps=16ms
1/162fps=6.1ms
1/200fps=5ms
1/300fps=3.3ms
If you want to get more stats try installing CapFrameX.
You can select specific sensor like the cpu wait GPU time called GPU limit time.
You can also have access to raw FPS data without the averaging.
There is also stuff like CPU stutter and variance in frametime measurements to confirm your performance.