Sale of same Item with different MRP in the same store

Based on the information in the erpnext documentation…

If we use FIFO, ERPNext will reduce the quantity of the Item priced at X first and then Y. Our query is how will that effect the price of items. For example, when we have item X with the following scenario how is the price not changing during the sale

First buy… Item X - Qty 2 - Price 20.00
Next buy… Item X - Qty 5 - Price 30.00

When we have a sale of Item X - Qty 4, technically we should have…
Item X - Qty 2 - Price 20.00
Item X - Qty 2 - Price 30.00
Total Price… 100.00

but now we get Item X - Qty 4- Price 20.00 = Total Price 80.00

Can you advice how to achieve this scenario, or can we achieve this in erpnext.

Any possible option to get this done in Frappe Store module?