Having spoken to Liam in support about this, he suggested mentioning it on the forums here to see how many others would benefit from an enhancement to the shipping manager as below. Apologies in advance for the length of this post, its tricky to explain concisely but please bear with me and comment if you think it would be a benefit!
The crux of the functionality I'd like is the "Catch-all - hidden until this becomes the first available shipping method" option to be available even when assigning specific shipping codes to the method, rather than only being available when the "All" shipping codes option is selected so you can present a single shipping method to the customer even though more than one may technically be applicable.
This would help us (and I suspect quite a few others) because most of our UK shipping is done via Royal Mail First Class large letter / small parcel, which we calculate by weight. However, as a large letter is limited in terms of how thick the package can be (25mm) some of our light but bulky items need to be shipped as a small packet, whereas a product that's exactly the same weight but thinner can go via one of the large letter prices. In this scenario a single by-weight shipping method doesn't work very well as you're always under/over charging and trying to balance it somewhere in the middle so you don't lose out.
To try and combat this in Bluepark I first assigned 3 different Shipping Codes to our thin (T) / medium (M) and bulky (B) products.
I then set up 3 Shipping Methods as below (I've listed which shipping codes apply to which shipping methods in the yellow box) plus a catch-all which sends as the more expensive small packet regardless of how light the order is. The 3 shipping methods all have similar pricing structures but the step up from large letter to small packet is triggered at different weights in each based on how much of each product type we can ship as a large letter before it becomes too bulky, so for thin products the large letter weight might be the full 750g threshold before going to small packet, whereas the bulkier methods trigger small packet at lower weights to compensate.
Shipping 1.jpg
The Thin "T" and Medium "M" products are assigned to the bulky shipping methods to cater for a mixed basket, so the bulkier shipping method still applies. If you only assign the one shipping code to each method, even a small / light mixed basket goes to the catch-all small packet only method which overcharges quite significantly because 9 times out of 10 it doesn't actually need to go as a packet.
With the methods above in place the problem now arises when a customer orders just Thin and/or Medium products, where they get presented with 2 or 3 shipping methods to chose from at checkout as in the screenshot below
Postage 2.JPG
If the Medium and Bulky shipping methods could have catch-all logic assigned so they only get displayed if they're the first applicable shipping method, then we could have nice granular shipping calculations whilst displaying only one shipping method to the customer and not an unsightly / confusing list of apparently identical shipping methods to chose from.