I'm confused about iPhone image sizes

lateapex used Ask the Experts™
IOS app targeting profile view for iPhones only. I have some background images.   xxx@2x.png  is ~ 333kb, xxx@3x.png is ~ 1.2mb. When I realized the size of the 3x, I loaded the 2x version into both the 2x and 3x slots in my assets. I run the app on a 5s phone and a Xs Max simulator. I see no difference using the original big 3x image vs the smaller one.

These background images are simple illustrations, not a great deal of detail.

Please help me understand this and is it okay to just run the smaller file in both slots?
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If your eyes cannot discern any differences, you should use the smaller file for more efficiency. Most likely, the bigger file has extra details if you zoom in really far, but as it's a background for an app, no one will ever do that.

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