For me personally, I only have a couple FOs that I have had to change wicking in and it's b/c they are thicker FOs. All of my others I am able to use the same in wick in the same container. I wicked up 1 size w/those FOs and haven't had any problems. I purchase almost all of my FO from 1 supplier which may also contribute to only using 1 wick size per container. I would start by testing 1 FO in 1 container with a few different wicks/sizes. See if any of them work for you and go from there. If it drowns, go a size bigger, if it soots or smokes try a size smaller. Trial and error. I started by getting a few different types of wicks and using the supplier's wick guide. I bought small packs of wicks in the recommended size, size larger & size smaller. I tested the same FO w/all the wicks to see which I prefered. Then I test that same wick w/each new FO I bought. Very rarely I would have to adjust the wick. It's not as scary as it seems!