It's the 2" diagonal causing you trouble I think. A 1.25" prism diagonal has the shortest light path, which gives 45mm extra in travel (back focus) in my scope. A 1.25" mirror diagonal is less in travel than that but more than a 2" diagonal, which means you should be reach focus with your eyepieces. Try a cheapie mirror diagonal if you can and see if it works.
Matt
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