Table Rate Shipping – bundle issue when multiple classes

I am a clothes shop and have set up 4 shipping classes(cost price/bundle price); light (£4/£1), mid-weight(£5/£2), heavy (£6/£3) and very heavy (£7/£4).

A customer could for example order 4 items one from each shipping class. I want to charge them the ‘cost’ price for the very heavy item (as its most expensive) then the ‘bundle’ price for all additional items).

Therefore if the customer had 1 item from each class in their basket i would want shipping to be:
very heavy cost price + heavy bundle price + mid-weight bundle price + light bundle price
£7 + £3 + £2 + £1 = £13

I am currently however getting cost price for every item so its:
very heavy cost price + heavy cost price + mid-weight cost price + light cost price
£7 + £6 + £5 + £4 = £22

Bundle price only kicks in if it is an additional item in the same class as another item in the basket so for example if i added another light item to the basket i get the following:

very heavy cost price + heavy cost price + mid-weight cost price + light cost price + light bundle price
£7 + £6 + £5 + £4 + £1= £23

Is it possible to achieve the results I need as set out in the first example above?

Current settings are:

Condition: per item

Title: UK Shipping
Identifier: UK
Zone:UK
Shipping class: Very heavy
Based on: Item Count
Min:1
Max:999
Cost:£7
Bundle:£4
Default: Unchecked

This is repeated for every shipping class with only changes applying to the shipping class, cost and bundle options.

Shipping Class Priorities are set out as:

Shipping class/Priority
Very Heavy/10
Heavy/9
Mid-weight/8
Light/7

Hoping you can help. Thank you