If you use 16px, the 1.5 line height I use for paragraphs becomes 24px, which ties again with the multiples of 6 rule again. So your lines are actually 24px hig

If you use 16px, the 1.5 line height I use for paragraphs becomes 24px, which ties again with the multiples of 6 rule again. So your lines are actually 24px high, if you then use maybe 48px for spacing around your blogpost, things look balanced because they're even.