Usually when experienced mixers buy flavors, they read up on them to get a feel for what to expect. Unless you have unlimited resources, you have to figure out why to buy this brand over that brand, and that’s where flavor notes/reviews from others come in handy.
Once you’ve done this, you already have a feel for what it is you get, what the flavor is used for, how strong or weak the flavor is, whether it’s a supporting flavor in recipes or a main ingredient (or both).
Then when you’ve ordered the flavors and get them delivered, the first things you should do is a) add them to your flavor stash and b) make some test samples with different % (based on the company’s suggestions and flavor notes you’ve read).
Once you’ve tested them, you take some notes and you’ll be able to figure out at what % to used those flavors. An additional advantage of this is that when you see a recipe from someone else, you’ll already be able to judge whether it’s a recipe you might be interested in or whether the flavor is used inappropriately (for your taste buds).
As long as you don’t have a grasp of what your flavors are like, the recipes that you’ll make will be hit and miss, because taste is very subjective. Some may like a flavor at high % in a recipe while that really doesn’t work for you.
Flavors used at very low % (e.g. your 0.2%), may be extremely potent flavors, or just there to support another flavor in the recipe. E.g. a touch of dragonfruit may be used to make a strawberry flavor more rounded without giving the recipe any hint of the dragonfruit itself. In other recipes you may see that same dragonfruit used as a main flavor at a much higher %.
You really have to read about and test your flavors a lot to have a good understanding of how to use them. With so many different flavor companies and even within a brand you may find different flavors of the same (e.g. tpa strawberry, tpa strawberry ripe, etc), it just takes a long time to really get the hang of everything. To make things even more complicated… it’s not just what a flavor tastes like that is important. Also the composition of a flavor is important. Some flavors may contain Ethyl Maltol for example, a substance used to sweeten flavors, but it also has the effect of muting flavors and taking the edge of sharp notes in a recipe. So combining a few flavors that taste great separately, may end up not being so good when you add them together. This is why people keep saying to read a lot, and when you think you’re done, read some more.
Don’t let that scare or stop you though. There are a lot of people who don’t even care about these things. They just browse existing recipes, get the flavors for those recipes and make them just like that without fiddling with it or creating their own recipes. It’s all up to you what you want to do with it, that’s the great thing about DIY.
Going about it this way is ideal when you start mixing your own e-liquids. The knowledge about your flavors will build up over time.