Static meshes vs Instances - a strange behaviour

Hello everyone.
I recently noticed a strange behaviour that I don’t fully understand. Lets say I have 1000 trees in my scene painted with the foliage painter. As far as I know the foliage tool uses hierarchical instanced meshes for a better performance. But when I place the trees manually as individual static mesh actors the performance is much better compared to the foliage tool. That doesn’t make any sense to me.
Then I made a test bluperint that spawns a grid of trees (lets say 30x30=900 trees) with a boolean to either spawn a static mesh component or a hierarchical static mesh instance. And again the same result. The difference is not as big as compared to the foliage tool but still I have a higher fps with just regular static mesh components. How?
Did anyone else noticed this behaviour? Any explanation why is an instance slower than an individual actor? Thanks.