Look at the text field where you’re saving the Rich Text Element’s (RTE) output, it will have the image something like [460px path/img/url.jpg](I’m doing this from memory, apologies if it’s not exactly that.). You can change that absolute size reference — 460px — to a percentage — like 50%.
By the way, I was soooo frustrated by the RTE that I figured out a whole converter to handle images better than RTE.
