In order to make time for writing I must give up working or gaming...
I've always played it that way. You have to kill troops whose combat value equals the number you dialled on the battle wheel. They particular combination is up to you.
So if you won a battle by dialling "4" you could kill 4 regular units or 2 Fedaykin/Sardaukar.
Using the Advanced Rules, if you dialled "4" but only paid 2 Spice, you would have to kill
6 regular units (2 supported, 4 unsupported)
a combination, such as 1 supported Fedaykin/Sardaukar, 1 supported regular unit and 2 unsupported regular units