I just looked and it appears you did solve the small image with continued reading part. As for the full post view, the image will be the size that the original image was but will resize to fit whatever container it’s going into. So if you did an insert of image into your post below the “Continued Reading”, you will need to create a new image for this that is the size you want. The image you have there is 1024×1024 and see you forced a resize to 400×400. If this is the size you want for that one, then you would create that as that size and then upload it and use that sized version.