وَإِنْ شَاءَ قَوَّمَهَا، فَأَعْطَى عَنْ كُلِّ مِائَتَيْ دِرْهَمٍ خَمْسَةَ دَرَاهِمَ
Translation: Or, if he wishes, he values them and gives five dirhams for every two hundred dirhams of their value.
Qawwameha means to assess the aggregate worth of the horses. The levy is then calculated by value rather than headcount.