Controlling the Tax Classification on an I-Procurement Requisition

We would like to be able to control the Tax Classification on an I-Proc Requisition.

On the client setup the default Tax Rate is 20% Non recoverable VAT but Tax Conditions have been defined to default 5% VAT and Exempt VAT based on certain Nominal Account ranges. For example a Tax Condition has been defined to default 5% Reduced VAT for the 'Electricity' nominal account. In the current setup the Tax Classification of all Requisitions is the default tax of 'Non Recoverable 20%' but then the ststem overrides that tax based on the Account conditions.

The objective is to default the correct rate of Tax, ie '5% Reduced VAT' as the Tax Classification.