That's a really good question Poider...
On my SCT I had one right up on the corrector plate; on my main AP scope my Bhatinov sits on the end of the dew shield, the one I'm about to order for my Vixen 130 Newt won't sit on either really coz... it's a newt...
I get excellent focus results either way...
So, my best guess is no... it doesn't matter but, I'll be interested to see what other more knowledgeable folk have to say on the matter...
Cheers
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