FMSs work in different ways. On ours, you can enter descent winds for 4 levels that come off the flight plan, but these can be forecasts nearly 24 hours old! I believe some wash out the last cruise wind down to zero during descent. It's not really critical, you're only in the descent about 20-25 minutes, and other factors come into play, like track miles to touchdown become more important.
It's not a bad idea to get to know your performance. Calculate a desired end descent position and altitude. See how your aeroplane descends- work out 3x alt in thousands, probably +10, allow a bit for wind, and see how that does it. It was fine on basic 737s.