Acen sits next to 3 phonetic neighbors — Asen, Ason, and Jason are the closest matches by sound. Most share Acen's Acholi/Luo-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"first-born son"
Similar sound: These names share phonetic patterns with Acen — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Acholi/Luo origins, giving them the same cultural heritage as Acen.
Rhythm: Acen is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.