Appropriate method for allocation of under- applied or over- applied depend on :-

The treatment of the under applied or over applied overhead depends on the materiality of the amount. If it is immaterial it can be moved to cost of goods sold. If it is material, it is apportioned among work in process inventory, finished goods inventory, and cost of goods.

M.O.H will be applied or allocated to inventories on hand ( part of it will be sold (C.G.S) and the remaining will be ending Inventory for the period ) , so the over or under applied M.O.H Will depend on both C.G.S and  ending Inventory

COGS only because its cost budget and applied to cost of goods sold only.