Shipping Troubles

Site URL: http://www.jnesbit.com

I'm trying to get some advice on how to improve my shipping options on my website. We sell artwork, and I currently use the shipping by weight option. I have a broken (but workable) system currently in place based on a metaphorical "weight" assigned to products to help the shipping costs scale roughly to the size of the order. For example, one small 8.5x11 "weighs" 1 lb., one 18x24 "weighs" 2 lbs.; the shipping price bracket from 1 - 4.99 lbs is $7, after which it increases from 5 - 9.99 lbs. for $10. (I've included a few screenshots to demonstrate how this is implemented both in the shipping section and the product variants section)

I'm interested in using the calculated rates options to simplify the process, but I'm unsure how to make it work with my products. Sometimes products can be shipped flat, but other times they can be rolled in tubes, and this is largely done at the discretion of our in-house order fulfiller. Larger-quantity orders are typically shipped in tubes, whereas smaller orders are typically sent flat. Is there any solution to where people could be paying more accurate, proportionally-scaling shipping rates?

For example, the shipping options help page suggests listing a 24x36 as 3"x36" in order to fit into a tube. This is a great tip, but does the calculator understand that, if multiple products are ordered, they could be grouped into a singular tube?

If you view one of the art products on our website, you can see the problem I'm running into. We offer so many variants (and some materials are drop-shipped from the oversize printers directly) that it's difficult to have a system that scales well and is generally effective.

I'd greatly appreciate any advice you have!