I have set up a simple store and got one type of product working fine. They weigh 100g. I have added another category of product that weighs 250g. The problem is that due to the size of the products being quite different, and postage in the UK varying by weight AND size, it's hard to work out a costing method.
For example 3 x 100g costs less to ship than 1 x 250g product due to the size of the latter. The Delivery table by item is perfect for one item type, but neither that nor by weight seem to do what I want with mixed product weights.
Can anyone suggest a way of doing this?

Here's the table of costs for both product types:

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HTML Code:
Product 1                  Product 2
Qty	P&P	weight	   Qty       P&P	weight
1	£2.50 	100g	   1	     £4.00 	250g
2	£2.50 	200g	   2	     £4.50 	500g
3	£3.00 	300g	   3	     £8.50 	750g
4	£3.00 	400g	   4	     £9.00 	1000g
5	£4.00 	500g	   5	     £13.00 	1250g
6	£4.00 	600g	   6	     £13.50 	1500g

Thanks for reading.
(I've searched through the forum and not found another query on this)