I am not on 11 yet -- bought new systems on Black Friday and they just came in. Won't set up mine until after my trip.
There might be a confusion in your settings or what you are trying to do. For here, the importance of the size is the file size, not the picture size.
Basically pixels are when you take an image and make it into small bits -- the pixels. so 2560x1440 is how many small dots you have across say your computer screen. You can reduce those pixels down quite a bit without sacrificing detail to human vision. That also reduces the file size because there is less information to store.
Often the easiest way to reduce images is to convert to JPG, for my pictures I still have to reduce further. If you have the ability to send to yourself via email or have a share button, it will most likely be postable here.
Maybe this more technical discussion will help?
https://www.sony.com/electronics/sup...icles/00010755