I think you'll find 30cm spaced omnis will provide too narrow an image for nature recording. Placing the omnis at an angle will do very little (if anything) to widen the image, since by very nature, omnis aren't directional. The larger 66cm spacebar would work better for this application, but even then, you're probably better off mounting the mics on separate stands for greater control of the stereo width. The only way to work with Omnis in a more compact setup would be to use a Jecklin Disc.