Why does a picture saved as an ipone home page background look magnified?

I save a wallpaper to my camera roll (like say one of the many shelf wallpapers so your icons on your home page look like they're sitting on shelves) and once I do and return to my iphone home page the wallpaper looks like it's magnified and larger so the icons don't line up on the wallpaper's shelves. Same with a photo used as my home screen wallpaper background. Once I save it it now looks larger when I return to my home page. It does not do this when I save an image as my Lock screen background. When I go to the lock screen it's the exact size it was when I was looking at it in my camera roll. Why?

It magnifies to fit the screen of the phone

It seems that your pictures are slightly smaller in dimensions compared with other standard wallpapers. You can download the shelf wallpaper for free for your iPhone on the internet and copy the picture to your computer into a Wallpapers folder then sync the folder with iTunes. When you choose to set the picture as a wallpaper don't adjust or zoom in (just add it as a wallpaper as it is).

Maybe it's the size problem
if your photo's original size is smaller than the wall paper
then if you choose that pictrue it will be heightened

So I suggest you to change the size but reserve the definition
you can use a photoshop to reach this effect
and you can also use other photo handle tools
hope this will help you