down on the bottom right of the screen are X,Y and Z with a box with a %number (probably a low number). If the large picture is full screen when you resized it, the picture will get smaller, but the screen view stays the same. Go to the % box and increase the number to make the picture larger (I usually work between 70 and 90%). If you have a mouse with a wheel, you can hold down the ctrl key and scroll whe wheel up and down to increase/decrease the window %.
I don't use the open file button, I use import. You will still the the link or embed image screen. Choose embed.
Hope this helps
Mike