4 days is plenty long to get hooked back on H again and therefore need to basically re-do your suboxone induction. I find even 2 full days of straight use will almost put me right back where I was prior to taking the Subs.
Also I wouldn't say the COWS scale is useless. Is it perfect? No, but its the best resource available to judge w/d. Is there a way someone can score you on it, rather than scoring yourself? It is designed for a health care worker to score other people, not for people to score themselves, so that is the only true way to get an accurate score. Its easy to be a little more forgiving to yourself when scoring it and judge things worse than they actually are, while someone else will be unbiased. You have to factor in the size of your habit when using the COWS scale, too. A 2 G a day IV heroin habit probably means you need to wait until you're above a 25 on the scale(plus if you are more prone to PWD, its best to wait to that point). Someone doing 100 mg of probably only needs to be slightly sick, just on the mild range.
No one is going to have a definite answer because its too variable from one person to the next. If you are really concerned of the PWD, I'd wait as long as possible and keep the dose very small to start.