What you can do actually you can make an overlay first and put your image inside (material), please do put sizes exactly like 1024*1024 or whatever.
After this wrap your overlay with a size box-> in settings fit the horizontal aspect ratio 1 for min max
this would always keep your image proportional whatever device is
Think it should solve your problem of scaling without any use of code or image resizing.
Let me know if you can get it work.