Hi Fom my experience horse riders tend to maintain thier lumbar spine in an overly extended (lordotic) position. This produces chronic nerve root compression and produces intermitttent leg pain. Try riding in a neutral pelvis (reduce the lordosis) and monitor what happens to you leg symptoms. Your symptoms improve with constant use as you move your pelvis with a range of activites and this limits the nerve root compression but does not give a lasting solution. I am not a bit fan of myofascial trigger points and find these points resolve quickly by addressing the cause.
Hallamshire Physio