[LostOnTheLine]

Is there any way to adjust other settings aside from the width?

Before I started using Sigil I was unzipping epubs, using BIMP to batch convert & shrink images in GIMP, turning wide images, then re-zipping them. I generally batch convert by the height rather than the width, this is especially necessary when there are wide images that have been rotated.
I also use JPG with quality levels typically set to 90, 1x1 Subsampling, Low-Halo interpolation for the scaling, float-point DCT, etc. I generally sacrifice conversion time for better quality/size because it can work in the background.

Using the plugin I was very disappointed with the size difference (I typically shrink a 30-40MB ePUB down to 4-10MB), The Plugin made the images smaller than my old method & the 37MB ePUB I was testing on only got down to 18MB despite the images being smaller. If I could adjust at least the quality setting that'd make a huge difference as I'm fairly certain it's keeping the quality level at around something like 98% which is a lot more than I personally need.
When calibre converts my ePUBs to KFX the size ends up near to what I was getting using this method, I'd just like to have the ePUB at that resolution & AZW3 as well

Since the "maxWidth": "1000" is set via the JSON it would be nice to have other options, like "maxHeight": "1200", "Quality": "90", "Interpolation": "LowHalo", "DCT": "FloatingPoint"

I appreciate that this exists, I just wish there were more options.