Sublimated or All-Over mockups allow you to display your designs on the entire garment. Instead of duplicating your pattern to fill the garment, it will cover the whole mockup.
This is how a sublimated t-shirt mockup looks like before adding your file, note how the placeholder pattern covers the entire fabric, this is where your design will show.
For a better display of your design, upload your file in the suggested size of each mockup, for this t-shirt mockup, it is 1600×1800 px.
The shape of the t-shirt is the area of your design that will be shown on the mockup. Have a look at the full process:
And this is how it looks like after you upload your design! Note how your artwork covers the full garment, even the edges of the neck and the sleeves will show as if they are printed with your design.
All sublimated mockups work the same way, have a look at this tank top mockup: