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One thing I've seen with metal angle frames is they are not strong in torsion. A stronger frame work connecting the two cages might help. Would serve to reduce twist incurred in changing altitude.
As Tnott mentioned, might the poles be a little thin? The sum wieght of the secondary cages plus the connecting frame and its 'spread' is not the same engineering as a single cage for such poles.
Could the tension in the spiders be a source of deformation in collimation? Changes in moment at the cages in the change of alt. position could cause variation in the tension. This might be a symptom of the poles, though.
Maybe a stouter centre brace around the middle of the OT would be a simpler solution to the deformation.
Just trying to tickle some ideas and thoughts.
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