First..that's just your opioid cravings saying take the other two. There is no way you need to take 20 mg of sub. And it won't get you high. Anything over 8 max is a waste.
If that 4 doesn't hold you and you truly feel *physically* sick try dosing another 2 mg. You want to be physically ok to start a taper. Not "high" but not experiencing symptoms. Shouldn't be sneezing, or eyes watering or RLS, or nausea/vomiting...you get the idea. Just mental cravings you can get past. Most important thing with cravings--remember it's just a thought. It only has power when you feed the thought and dwell on it and such...do the best you can to "change the subject" in your own brain.
Now. If you manage to be ok on 4 mg, or 6mg then continue like this:
Before bed take another 4 mg. (Unless you recently took that other 2 mg in which case take 2 more mg)
That's 8 mg for the day
Tomorrow start in the morning with 2 mg. (There will still be some from yesterday in your system)
Tomorrow night take 2 mg.
3rd day take 2 mg in morning.
Take 2 mg at night only if needed
4th day. Take 1 mg in morning.
Take 1 mg at night if needed
5th day try and skip. If you can't take then take no more than 1 mg.
6th day. Evaluate from here. If you're ok--and most people who go into detox on similar 5 day schedules are--then stop. If you really can't, take the absolute minimum you can --0.5 or 0.25.
This taper doesn't quite use every mg. That's because most of us feel better when we know we have something to take away the sickness. When we run out it's like panic time lol
Good luck. This is an example quick taper with what you have available. You can alter to suit you but stay as low as possible. And off in no more than 10 days.