Maximum distance of a symmetric rank-two tensor to rank-one tensors

We investigate the maximum distance of a symmetric rank-two tensor to rank-one tensors. An equivalent problem is given by the minimal ratio of spectral and Frobenius norm of a tensor. For matrices the distance of a rank k matrix to a rank r matrices is given by the singular value decomposition, but since there is a lack of a fitting analog of the singular value decomposition for tensors, this question is more difficult in the regime of tensors.