Allen sits next to 4 phonetic neighbors — Alan, Allan, and Alain are the closest matches by sound. Most share Allen's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"handsome, cheerful"
"brave warrior (later folk etymology)"
"Yahweh is merciful"
"home ruler"
"twin"
"God is my judge"
"gatekeeper, doorman"
"God is gracious"
"dispenser of provisions, household steward"
"hollow, empty"
"Hugh's settlement, town"
"enthusiasm, ardent"
"great brightness, sea circle"
"burdened, laden"
"wise person"
"dark warrior"
"healer"
"defender of men"
"from the island of Rhodes"
"of the forest; woodland"
"increase, growth"
Similar sound: These names share phonetic patterns with Allen — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Celtic origins, giving them the same cultural heritage as Allen.
Rhythm: Allen is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.