This paper describes a technique for realizing a high-rank channel matrix in a line-of-sight (LOS) multiple-input multiple-output (MIMO) transmission scenario. This is beneficial for systems which are unable to make use of the originally derived MIMO gain given by independent and identically distributed (i.i.d.) flat Rayleigh fading channels. Typical applications are fixed wireless access (FWA) and radio relay systems. The technique is based on optimization of antenna placement in uniform linear arrays with respect to mutual information (MI) for pure LOS channels. Both the case where the channel is only known at the receiver and the case where the channel is known at the transmitter and receiver are treated. By introducing a new and more general 3-D geometrical model than that applied in earlier works, additional insight into the optimal design parameters is gained. We also perform a novel analysis of the sensitivity of the optimal design parameters, and derive analytical expressions for the eigenvalues in the pure LOS channel case, which are valid also when allowing for non-optimal design. Furthermore, we investigate the approximations introduced in the derivations, in order to reveal when the results are applicable, which turns out to be for most practical situations. The LOS transmission matrix is used in a Ricean fading channel model which incorporates spatial correlation between the non-LOS components, and performance is evaluated with respect to the average MI and the MI cumulative distribution function. Our results show that even with some deviation from the optimal design, the LOS MIMO scenario outperforms the i.i.d. Rayleigh scenario in terms of MI.