Is it true that ...

Larger angle prisms "favor the large trees?"

No. Used correctly, any angle gauge picks trees with exactly the same relative frequency as any other angle gauge. If a 40 BAF prism is picking up 20% large Douglas-fir and 80% small Douglas-fir then a 100 BAF will pick up exactly the same percentage of each of them in the long run.

A larger prism will pick up fewer trees, but exactly the same percentages of any type of tree as any other prism. This different selection is just a myth. It probably started because using an angle gauge picked large trees more often than a fixed plot (which is correct), so people probably reasoned that "a larger angle must intensify the effect." Not so.