With the the Lychee Peach V1 you made, as posted above, I would lower the FA Peach by half to 3%. In my experience 6% is too high and will mute. I would also drop the FA Lychee down from 8% to 1%. FA Lychee at 8% is serious overkill IMO. I believe that would be a good starting point for both + the CAP Sweet Strawberry is fine at 1.5%.
The reason it's muted is because those FA flavors are too high IMO. FlavourArt flavors are more concentrated than TPA or CAP for example so you need to use less of the FA.
I think(?) OP subbed TFA Peach, and FW Kiwi, for the FA called for in the screen shot. At least, that is what I interpreted, based on the OP's list of available ingredients in their first post.
While still "higher" percentages; I don't see them being in the "muting" range. Just my opinion...
My take on sweeteners, for someone starting out, is very simple ... don't go there until you understand how and when to use them. I do not use sweeteners at all. My reasoning is very simple .. there are many many flavors that are already sweet and knowing how to balance a recipe will get you sweet minus sweeteners. Try to make some recipes without any. There are plenty of great recipes here and out there. YMMV
I generally agree with this; especially with TFA Sweetener... as it contains both sucralose,
and maltol. CAP Super Sweet is a better choice; as it is only sucralose. Maltol is a serious flavor killer, and you are right, it is already present in many flavor concentrates.
My only reservation, in
@StaticVaporSA's case, is they are comparing (trying to simulate) "syrupy" commercial e-liquids they are familiar with. I don't see how they can do that
without the use of a sweetener (preferably CAP Super Sweet
).
Instead, I might be inclined to suggest this:
Start with only the fruit flavors (no sweetener, or coolant). Get those tasting as intended... knowing the "sweet, syrupy" aspect will be missing. The mixture, as is... without sweetener, may taste dry/thin/or incomplete. That is okay. You are only looking for the right balance/ratios of one fruit, to the others, at this point.
Once the fruits are balanced as desired; then, begin adding sweetener, about 0.5% at a time... until desired sweetness is achieved. Then, repeat with coolant.
Note about the "Black Ice:" I am not certain, but it appears(?) to be a
20% concentration of WS-23, and not the more common 30% concentration we are used to, here in the U.S.. As such, it is not unreasonable to expect, that half again as much would be required for the same effect.
I would also say to
@StaticVaporSA; that neither sweetener, nor WS-23/Black Ice, require any steeping. Therefore, they can be easily be added to an otherwise "finished" mix (to taste) without adding additional steep time.
I have found from my experience, that fruit concentrates can be true "shake & vapes," especially when used at lower percentages. However, many still benefit from a short steep (+/- 72 hours). Fruits, in particular, can have an initial chemical/artificial taste to them, and this becomes more noticeable the higher the percentage used (it is often one of the signs that you are over-flavoring).
First, try using less. If the flavor is too weak at lower percentages; let it rest for up to a week. This often allows the unwanted notes to dissipate.
If the harshness, or artificial/chemical notes are still too unpleasant, you can try to breathe/vent the mixture. ("Breathing" is the act of leaving the mixture sit uncovered
(no cap, and no drip tip) to allow the volatile chemicals (like ethanol) to evaporate.) Let the mixture breathe for a couple of hours, to overnight, and retest. If, after that time, nothing improves; further breathing will not be beneficial. (Breathing can be damaging to more aromatic flavors (many lemons, some strawberries, etc.); so, always, use sparingly... if at all.)
Finally, if lower percentages are not an option, and breathing hasn't helped; the addition of a sweetener can help to take the sharp edges off. Start with no more than 0.5%, and incrementally increase (I would personally go up 0.25% at a time) the sweetener as needed. Do watch for flavor muting as you do so.
These are more advanced mixing techniques. They can bugger up a mixture as fast as fix it. So, go slowly... test vape frequently... and STOP if (at any point) it seems to start to go sideways (additional tweaking won't fix it; start over). Read this Myth Busting article (some excellent general new mixer advice) for context.
Also, mix small test batches... 10mL should be plenty... 5mL might even be enough for the initial fruit-only mixes. Conserve your ingredients. The initial goal should be to get an enjoyable mix. Creating a surplus supply should wait until you have a known "successful" recipe. Small batches are also easier to throw out (vs. feeling like you have to "fix" them).
And my final piece of advice: take notes on everything you do. Note, every mix variation, every treatment you apply. It will save you making the same mistake twice. And, it will allow you to repeat successful results. Nothing is more discouraging, than to get it "absolutely perfect," and never be able to repeat it. Notes can help prevent that.
Best wishes as you begin your journey of DIY... and welcome to ECF! 
