तस्य द्विरथोत्तरा वृद्धिरैकविंशतिरथादिति ॥ कZ_१०.५.१५ ॥
tasya dvirathottarā vṛddhir aikaviṃśatirathād iti
तस्य (समव्यूहस्य) वृद्धिः द्विरथोत्तरा; एकविंशतिरथाद् इति।
Even-number increments preserve bilateral symmetry (left/right) and keep wings balanced while scaling the formation.
A minimum viable baseline size for this formation family, from which standardized expansions are authorized.