pm, ‘Computer Red’ was a clever device for its time; it calculated many intercept functions and communicated with missile. Some of the functions included ‘angle between courses’ (ABC) – the intercept angle and head / tail aspect, and also in conjunction with the radar provided a target closure rate even in a jamming environment. I recall that many years later, this function was ‘invented’ in the US as angle rate bombing, but it was actually the kinematic ranging function of AI 23.
FS had an intelligent fuse as you describe, using two rings of windows to determine the optimum position to detonate the large ‘hand grenade’ warhead – next to the cockpit. FS accuracy was such that most targets would be hit, thus the back-up contact fuse would be used.
RT had a slightly different fusing arrangement, using 3 small windows and split mirrors to provide the tail aspect delay similar to your description, but also the much earlier head-on fusing. The actual fusing timing / geometry also differed from FS, as RT used an expanding ring warhead which was best detonated at the centre of the aircraft – it was designed to saw through the structure.
AB, yes from memory, RT seemed to at it best when given a challenge; perhaps that is why the head-on performance was relatively good.