By default, iOS’s@2X -> @3X ratio is 1.5 times. For example, if your design page size is750x1334, its @3X will be scaled to a width of 1125. But we know that the resolution of iPhone XS Max is 1242×2688.
In some cases, if you want @3X to be the size of 1242, there are three ways to set it up, as shown below:
Select any desired layer and tick “Set iOS @3x width to 1242”:
Select your desired assets on the right panel and tick “Set iOS @3x width to 1242” below:
Download all assets by clicking “Download” in the upper right corner and tick “Set iOS @3xwidth to 1242” on the pop-up panel：