I don't think there's a way to control image size based on the standard formatting RPoL uses for posting images (I could be wrong, but I've never seen it).
You might just need to resize the pic. The standard Windows photo viewer (and yes, this is both an assumption you're using Windows and the standard photo viewer) will scale the image to the size of the screen/window you're viewing it in. This is doubly true in most browsers, if you're viewing it on a website.
If it's a file saved on your computer, you can actually hover your mouse over the file in File Explorer, and it will show you what the pixel dimensions of the image are.
If you ARE using the standard windows photo view, try this (and feel free to ignore this if you already know how to do it):
- Upper left hand corner, there's the 'See More Options' button, represented by the three dots.
- Click it.
- Choose 'Resize'
- Choose 'C' for customer dimensions.
- Play around with either the Width of the Height (keep Maintain Aspect Ratio clicked so you don't distort).
- Click 'Save Resized Copy'
- I'd personally choose a new name or put like '01' at the end, so you have your original and your new one.
- Upload it to whatever photo/file share site you use (I'm lazy. I use Google Photos).
- See if that helps.