First of all, it is just as well to realize that no woman is completely symmetrical. Even women with two breasts often have a difference between left and right. To avoid disappointments, it is useful not to be too focussed on symmetry.
Having said that, it is of course nice if both bumps on the front are similar enough for no one to notice anything. That is what the Qups are for. They are very flexible in shape and conform to the (shape of the) bra. In most cases this leads to a nice symmetrical result. The shape is therefore mainly determined by the bra. It matters whether the bra itself has a clear shape, as is the case with pre-formed cups. The Qup then forms with the bra, just like your own breast does. That way you have the best chance of symmetry. If you choose bras that do not have its own clear shape, such as a sports top, then it is a different story. In that case, the sports top forms with the Qup on one side and with your breast on the other. Inequality then arises more quickly.
If you wear 2 Qups, it's a different story. Then you do not have to take into account a differently shaped breast and the difference in weight. The challenge of sliding then has to do with moving both Qups up and down because there is not enough support. In that case it is a good solution to wear a body, preferably with some sort of elastic support around the breasts. Then the Qups stay in place because the body around your midriff keeps everything together. The elastic support keeps the Qups in place, especially if you also sew them on tightly.
Anyway, what can you practically do when you feel like your Qup is sliding? Or if the shapes on the left and right are not quite the same? Our 3 tips:
Good luck with your Qup and finding your symmetry. And don't forget that noboby is as critical as you. Others often don't have any idea, especially after you've added a layer of clothing. People mainly look at your eyes and not at your bust.