I've only gone down to 40, never 20. My time is very solid from years of working with clicks, however, and I've used other tricks to help my time.
1. Setting the metronome to only play off beat 16th notes. Play 8th notes in between the off beats. It constrains you in a totally different way than the on the beat click does.
2. Similar thing but move the down beat on the click in your head mentally to the off beat 8th and then the "e" and then the "a". Got this one from Benny Greb.
3. Subdivide the beat by up to 19. Play whole notes all the way up to 19 notes per beat and be able to move in between any of them effortlessly. This will naturally lead into polyrhythms.
4. Play odd numbered phrases over 4/4 time and feel the shifting one underneath your superimposed time as the phrase resolves back to the downbeat.
All of these are challenging tools to help in your/our quest.
I'm gonna try the 20 bpm thing now