You don't have to be limited to small, medium, and large. You can specify a number of pixels (which will be used as the width, and height will be proportionate) if you want more precise control. 700 will be as wide as you can use on a profile page and you can experiment until you get it to appear exactly as you want it. While you can use the PREVIEW button on the edit page, when placing images you will not always see it precisely how it will look on the view page, so you may have to enter a number, save, look at the view page, return to the edit page and change the number …. several times before you're satisfied.
There is an additional parameter that you can use if you wish - that's wrap, with value choices of y (for yes) and n (for no). The default is n, which will stop the text, display the image with blank space to left and/or right of it, and continue the text under the image. If you choose y, then the text will fill the blank space alongside the image. The way you use it is under the caption line and above the }} you would put a line that says:
|wrap=y or |wrap=n