Lip tints fade unevenly because they're designed to be breathable, so they wear away faster where your lips move most - the center gets the most friction from talking and eating. Instead of powder (which can make it look chalky), try exfoliating and moisturizing your lips first, then apply the tint in thin layers and let each one set for a few seconds before adding more; this builds up color in a way that wears more evenly. You might also want to use a lip balm underneath as a base rather than primer, since primer can sometimes create a slippery surface that tint slides around on. If it's still patchy by afternoon, honestly those stains just might not have the staying power you need - some people have better luck with tints that have a bit more grip to them.