Watermark only specific image size

Hi,

I’m wondering if it’s possible to have watermark applied automatically to a specific custom image size. We have a custom size called “social” which is a hard crop of 1200×630 (the correct ratio for Facebook and Twitter). It’s the only size we’d like to watermark. Right now, we do this manually and it’s a hassle. Could we use this plugin to automate watermarking of this specific size only?

Many thanks,

Bira