[Plugin: Postie] Specify Original Image Size?

Hi,
I am a little rusty with my code, but I usually know enough to get by. I ran in to a problem today with Postie. Here is the blog I am working on https://www.1percentblog.com

I have set Postie up to post to my blog, after a few hiccups I have images posting too.
I currently have the Postie Options for images to custom, using this code:

<img class=”alignnone” src=”{LARGE}” />

Which works successfully in the page view, but when viewed in the archive/main page of the site the theme overrides the image size (as it was left unspecified by Postie), and distorts the image. I would normally do this: width=”500″ height=”394″ but I can’t do this if the image being posted is different each post. So my question is, how do I specify the dimensions of the image to the original size of the image?

On the site you can see the post “Testerquack” is displayed scaled down by the blog theme, but with correct proportions. While the post “Testpie” has been distorted.

Any help would be much appreciated!