Small amounts probably put your thought processes into a sort of "uncanny valley," where you can notice something is wrong, but not enough to revel in it.

It's like going outside with your zipper open, rather than with no pants at all:)

>for someone with such a high tolerance

I don't think that there's a tolerance with LSD. There's a learning curve, rather; it doesn't affect you any less, you just deal with it better.