FMC calculates TOD based on predicted wind, weight and required flight path/speed constraints. We hit TOD and close the TLs.
Generally, ROD = Deficit of Power / weight.
Given that this is intended to be an idle descent, deficit of power is determined by drag. Drag in turn is dependant on air speed. Thus ROD depends on air speed. We are probably well above Vmd therefore fly faster = more ROD, fly slower = less ROD
If this is a path descent and HW is higher than forecast, then your GS will be slower than usual. The planned ROD will tend to leave you low on the profile.
But if we (or the APFD) are pitching for path we will raise the nose, therefore we will slow down.
As we slow down, energy dissipation decreases (less drag) therefore our ROD decrease. (There is also some short duration trading of kinetic Energy for Gravitational Potential energy). But ultimately a lower descent rate, associated with a lower speed, can correct the geometry of the path.
At high speed energy dissipation approximates the cube of speed (power required = drag x tas, and we are up on the V squared bit of the drag curve). Thus speed changes are very powerful (badum, tschhh, I’n here all week) in modifying descent rate).
Hope that helps.
ps it may be easier to visualise of you think about a stong tailwind.