Kullen sits next to 5 phonetic neighbors — Cullen, Collin, and Kullan are the closest matches by sound. Most share Kullen's Scandinavian cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"hill, ridge, small summit"
"hay valley, from the hay hill"
"from Hesston (place name)"
"knife, cutler"
"fury, divine madness, inspiration"
"invented modern name, possibly blade-valley"
"supplanter, heel-catcher"
"strength, virtue, honor"
"child of the sea and wave"
"from Britain, Briton"
"modern blend of Jay and Gavin elements"
"the greatest one, supreme ruler"
"dweller by the rye field"
"son of Cadán, little battle"
"his name is God"
"angel, divine messenger"
"black, swarthy"
"thankful, God has heard"
"rising, ascending"
"strong man"
Similar sound: These names share phonetic patterns with Kullen — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Scandinavian origins, giving them the same cultural heritage as Kullen.
Rhythm: Kullen is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.