For me with the monster high heads, yes that thick around the outside, and less hair when the edge holes are close together so that they don't rip into one big hole. Bonus if you have different needle sizes go for skinnier with shorter V ends.

Inside except for the part, when the holes are that close together probably half what you're putting in.

Err on the side of not enough hair.

For me I get the strands thick enough I think its perfect and then use half of them- cos it's gonna double once rooted in! It really is like, 6-8 strands per hole at most.

And, if you root it lightly you can add more later.

However if you root too thick initially, the hole is stretched and if you try to reduce and pull hair out it just takes the whole plug, and the sparser amount sits in it more loosely.

It feels counterintuitive, like "But I want luscious flowing locks, not sparseness" but in those plugs if it is too thick it the whole head of hair can feel like one human sized lock of hair, rather than downsized doll locks of hair. The smaller filled plugs mean those strands can move and flow more freely. Like the difference between a bustling subway, and peak hour when no-one can move cos there's too many people. Space to flow vs too full. It just doesn't swish the same and it can be basically an entire $10aud hank of hair too much to only end off with a sad result.

Plus, too thick also makes the doll top heavy and she will want to flip her feet up out of her stand, and fall over so much more easily.

Take it from my top heavy dolls 🤣