If you're going fast enough, take the lane.
That way traffic behind you has to stay behind you.
If the corners are the only places where you need to cut in, then take the lane well ahead of the corner - sit in the middle of the lane or in the more-central wheel track. Avoid sitting in the outer-most wheel track, because that might encourage a car to pass dangerously.
Because you're taking the lane at the top of the descent, or well before your corners, then you have time to glance backward and see what's coming.
Your ears loose value on a downhill because of the wind, and the detection range drops. Also, vehicles are getting quieter engines and tyres than historically, and vehicles on the overrun can be very quiet.
Aside, I once had a diesel-electric locomotive sneak up beside me,
on a flat road with a railway to the side. That was educational.
The speed differential is what matters here - too slow and you'll just clog the traffic. If you can ride at or close-to the posted speed limit then a vehicle should be matching your speed. I routinely do 50/60 km/h descent on a road that is 70km/h at the top and dropping to 50 km/h lower down. Its not unusual to keep up with a car all the way down.
Your estimated 20 mph or 31 km/h might be a bit slow if the traffic is doing 50 km/h or more, so take it all with respect to your personal environment and risk acceptance.