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As far as I understand it for short focal length larger scopes a 2" EP is better as it allows the wider angle light rays to not be vignetted at the EP focusser entry.
For higher f# smaller scopes there appears to be no advantage.
I bought a 32mm 2" Kellner for my 10" F5 cheap on sale to see if it made any difference to viewing. Other than being a nice wide view lens and a lot heavier it was no better visually than my 20mm GSO Superview EP.
The real advantage with 2" IMHO is being able to attach the DSLR via a T Mount adapter to take pix.
Your mileage may vary of course ..
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