DO NOT import photos of 4,000 or more pixels on the longest side of the photo. Always keep it less than that. I generally go with about 3,800 pixels on the longest side of my photos.
1080 X 1920 apect ratio is for High Definition TV screen
1080 X 1.777 = 1920
1920 X .5625 = 1080
Those mathematical formulas will give you a perfect 1080 X 1920 screen image after importing photos, and you will not have to Scale Frame to Size. When zooming on the photos, I frequently use “Ease In” and “Ease Out”. Sometimes Linear works in special cases. It is entirey up to your taste, and what the situation calls for.
Does this clear it up for you? Good luck . . .