Interesting.
If you read the PrestaShop official documentation link I sent, you will find this:
You can add as many attribute-value pairs as necessary to one combination. You can only add one pair per attribute to one combination: it is impossible to have both "Color: Blue" and "Color: Red" in your pairs; if this is necessary, you will have to create new attributes, for instance "Primary color" and "Secondary color".
If it is working for you, I can't see any reason for you to change the way you are doing. But if it doesn't work, it's because it wasn't supposed to.