I can't keep a thick hemline without regular trims, it just doesn't happen, and I don't have thin hair. For me to maintain a thick hemline, I'd have to trim it every 3 or so months, six is too long. You may just need to trim less, but more often.
Everyone's hair tapers at different lengths, but I think very few people have long hair with a thick hemline naturally. Maybe very thick curlies, or very straight, coarse hair. The rest of us in-betweens, need regular trims to get that look.
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