It's funny you mention vaper's tongue bc that's a problem that plagues me frequently! I have always asked for, and vaped, really strong flavors thinking that would help with my vaper's tongue, but I'm learning since looking into this whole DIY thing, that I may have had it backwards this whole time! Wouldn't that be a great added bonus, less vaper's tongue bc I'm using less flavor! Could I really be so lucky? lol
I think it's very possible that you could be

. Different concentrates vary greatly in strength, and different palates vary greatly in their native acuitt, so talking absolute percentages isn't always very meaningful, but... I found, after a while, that turning the percentages down from what you'll find on a lot of sites (especially the site that can't be named) can actually increase your perception of flavor, and definitely, in my experience, leads to less vaper's tongue.
I think one important thing to understand is that the total flavoring you want to wind up with has to do not just with the strengths of the concentrates you use, but with how many similar or identical molecules the ones you se share.
Let's say I have a fruit flavor that I think is a fine standalone flavor at 4%. And I have a cream flavor I think is good at 4%. I can likely make a juice I will like with 4% of each, and not have it be over-flavored, even if 8% of either would be a nightmare. I might even be able to add a bakery of similar strength at 4% and be at 12% total flavoring with some strong flavors and have it be OK (though by that point I'd probably want to scale them all back some, according to the needs of the recipe, though not proportionally to the number used, and not equally, again depending on the needs of the recipe.)
On the other hand, let's say I started with that first fruit at 4% and then used two similar supporting fruits with it, of similar strength, with similar flavors. Using all three at 4% each might be just as bad as using the first at 12%, because they would either share identical molecules or have similar molecules that acted on the same receptors. This is the starting point for thinking about what people call 'layering' in mixing, and I think it's very hard to come up with successful "complex" mixes without bearing this in mind.
The thing is, it can be hard to know which flavors share similar molecules and hit the same receptors from their names, and even from substantial experience with them as stand-alones or in mixes. TFA is really good about posting their ingredients, so... speaking of coconut, their "Coconut Extra" contains a _lot_ of gamma-octalactone. Which of their other flavors do? Even with their transparency I don't know how to search for that information easily. I took a guess and found that their Sweet Cream does, but at such a low percentage that it by itself is not likely to stack badly with Coconut Extra. But what about other lactones? Can you tell if another lactone is going to stack badly with gamma-octalactone? I can't, that's for sure, off the top of my head... And what about other companies that only publish SMDSs?
So really, IMHO, the only way to deal with this is to go slowly, and start with conservative levels of flavors, especially when mixing them. And play with fewer flavors at first, and then combine combinations. Because, while it's not surprising that a coconut and a cream share a molecule, there are lots of cases that are surprising. And when you have eight flavors in a recipe it can be difficult to tell which two are stepping on each other. And they _do_ step on each other, all the time, which is what makes mixing fun, but also what can make it very frustrating.