We sailed with less mast rake than most, mega rake did not work for us, and probably the lowest spi pole in the fleet. What Phill describes was an issue solved by fine tuning the lower bridle wires for good performance to windward. It was quite visible when beating if these were not perfect, but not while using the spi as far as I remember. Pre-bend in the spi pole was our way of lowering the tip while keeping the compression strut at the same length.

Will be interesting to find out where the advantage is and how well it works.