Robotech Art 3 hints at it. Long story short: Mikimoto character designs and Hirano designs that are a very similar style match well with Macross, the mecha definitely resembles and is somewhat derivative of Macross (let's face it, the Garland is kind of a bike-Valkyrie -- even the head looks like a Valkyrie's head), directed by the director of SDF Macross and in a pretty similar style, and most importantly, Harmony Gold already had a license to use it.