I think that 1/8- 1/2A should mean anything smaller than A (.15). As many other have said it; Planes which are often designated as 1/2A are often powered by larger and smaller powerplants. However Planes designed for .15-.30 engines have more in common to .40 size planes than 1/2A.
I would prefer a forum spanning the A-.35 size planes (which I enjoy too). The topics with these planes would result in different answers.