I am doing this on an iPad 10.2 running ios11 importing RAW only files from the system gallery, not iCloud.
i just tried this again, it resizes everything to 1080 on the short side. I tried with raw files that have just been imported, as well as files that have already been edited with photoshop touch, which generates what seems to be full size JPEGs in place. I have even tried straight and simple JPEG images. However the resulting files always have 1080 pixels on the short edge. The only exception I have found so far is doing this with ipad screenshots, it works with the original size.
i am using a Sony a6500 camera.