I've never met an ajuga that isn't aggressive.

Dwarf Ajuga? I know of chocolate chip ajuga, bronze beauty ajuga, which are both small, but are equally agressive. Mabey you are talking about one of these? I grow the chocolate chip ajuga (which just started showing its pretty blue flowers two days ago), and it has doubled in size in the past year. If you plant small plants sparsly it would take years to fill in a large space. It just depends how close you plant them to eachother and to other plants. Im sure the larger bugle weed grows at the same rate, but the leaves are bigger so it seems to grow faster.