so you are setting the base rate and per item rate to £11.00?
This is the behavior i would expect if you set the base rate and per item rate to £11.00.
the base rate is the starting shipping rate that is applied to the shipping cost.
it is applied if there are 1 or more items in the cart as a flat rate
The per item rate is applied as a multiple of the cart quantity. Quantity * Per Item Rate
If you set both the Base and per item rate to £11.00, the shipping will be calculated as:
£11.00 + (Quantity * £11.00)