As you well know, the fact that 12 silent numbers can be sleeping for a lot more than normal dozens or columns do is just a reflex of the innumerable possible combinations forming clusters of 12 numbers.
The table layout has only six possible combinations of such possibilities.
I recordered a sleeping dozen created by 12 silent numbers that remained silent for 92 spins (I tried your same methodology several years ago taking a Marigny De Grilleau suggestion).
Don't know about 18 numbers, I think you can expect to get them silent for 50 or more spins.
More interesting is the study of the exact position of dozens or, better, lines (6 numbers) coming along the way in order to build a dynamic new even chance.
You'll have to wait the situations when the positions in the last three spins are different, then betting the remaining three positions. This is your trigger.
Since you won't bet when positions are repeating, you are excluding a large part of the random world and at the same time you'll be more confident that sooner or later at least one of the three remaining positions you bet will be filled.
In a word, you shift the problem from "what" (line) to "when" (position) and "how" (actual distribution).