How can I create Portrait game assets to have same with gap for both iPhone 7 Plus and iPhone X?

In my Unity game I made changed my Pixel Per Unit value to 243 since the height of a Portrait game for iPhone X is 2436. The game looks great and the asset sizes look just right on the iPhone X simulator. But when I change to iPhone 7 Plus I get considerable space on the sides and it gets worse when I change to the iPad. How can I make my game have the same width gaps for iPhone 7 Plus and iPhone X without making assets look stretched horizontally or vertically?

Can someone please help me

I don’t think this is possible since aspect ratio of these target devices are different. This aspect ratio difference between iphones and ipads has already been a headache and now iphone x made it even more complicated.