Odoo splits it up based on the ratio of the base price of the products of the combo to the sum of the total price of each individual products in the combo. For example, let's say we have two products A (priced at $100) & B (priced at $50). These are the individual prices.

Now let's create a combo product that uses this product and price it at $120. When the product is sold Odoo POS, tries to split it up based on its ratio.

So without the combo, the total price for both would be $100 + $50 which is $150 correct? So now let's take ratio of each product for this.

Product A: $100/$150 = 2/3

Product B: $50/$150 = 1/3

Now that we have the ratios, next, we apply this price ratio to the combo product which is $120. So here is the split now

Product A: 2/3 * $120 = $80

Product B: 1/3 * $120= $40

So the total here would be $80+$40=$120 which is the combo price.

The customer gets to see the split of the values for the products in each combo but the sum of the split will always equal the combo price.