Diy takes patience, trial and error. Fruits I have always found to be more of a challenge.
I have not followed your journey so I don’t know what gear or flavors you have, or what specific recipes you’ve tried. So don’t @ me, as the kids say, if I suggest something you’ve already tried.
Do SFTs of everything and test them in a good dripper at intervals over the course of a week or two. Know what you’re looking to add. You say tart. (to which the diy community always warns, tart is not easy to nab, so you’re trying to get a difficult result)
So find the central flavor, and the flavors that fill it out. My personal experience is that my recipe will end up predominantly one flavor, backed up with two or three at far smaller percentages to enhance the main flavor.
Some recipes are 10% total flavor, some are 5 or 6%. But one flavor will be more than half the total. And I have an unwritten rule that I’ll use four flavors, no more. If 4 can’t get me there, I’m using the wrong brand.
For example, I might use 7% of the main flavor 1% of the layer flavor ( which will be the same fruit, but the first may be the ‘sweet’ profile, the second might be the ‘ripe’) 1% of a contrast ( maybe watermelon if your main flavor is strawberry) and 1% of an accent (cactus or gummy).
And I do add a little sweetener because that’s how I like it. I don’t really count it as a flavor although it is calculated as one.
Also, I find that certain atties work better than others for different flavor profiles. Fruit does best, imho, in a cooler vape. Not too much air, not too little, and easy on the watts. Bakery can be good that way, but it’s better warmer and can stand up to a lot of air. And since big air is my thing - at least for now- I’m sticking to vaping a lot of bakery. Just saying, you can vape whatever juice you want however you want to do it, but it seems the delicate nature of fruit flavors gets lost in heat and big air.