Make Photo Iphone Wallpaper Size. Use the pixel size for your Apple product from the chart above. So you wouldnt be able to further shrink down the image.
The Perspective Zoom display option isnt available when Reduce Motion is on or when Low Power Mode is on. So you wouldnt be able to further shrink down the image. Google Photos wont resize your images but Androids wallpaper function will.
Before making any adjustments to screen settings find the perfect photo.
Select Crop tool by pressing C key. The best way to avoid such hassles is to use the exact sized wallpaper as per your iPhones model. It forces a minimum size of your image from the top to the bottom of the iPhone. To turn it off tap the Perspective Zoom button.