Over-absorption of overheads

A company budgeted to produce 3,000 units of a single product in a period at a budgeted cost per unit as follows: Direct costs = $17 per unit Fixed overheads = $9 per unit Total costs = $26 per unit In the period covered by the budget, actual production was 3,200 units and actual fixed overhead expenditure was 5% above that budgeted. All other costs were as budgeted. What was the amount, if any, of over- or under-absorption of fixed overhead? Answer Fixed overhead absorbed (3,200 units × $9) = $28,800 Fixed overhead incurred ($27,000 × 1.05) = $28,350 Over-absorbed fixed overheads = $450 Why isn't incurred overhead calculated using the actual overhead expenditure, which was 5% above the budgeted? Thanks