Since you’re on the subject of 30mm tube I’ll give you my input. I have the Leupold 3-9x50mm EURO-30 with the 30mm tube and have used it for only one season. I also have the Nikon Monarch Gold 1.5-6x42 with the 30mm tube and haven’t used it yet but have compared them side by side and I would have to say the Nikon is noticeably clearer between the two. So if you have a chance take a look at the Nikon Monarch Gold 2.5-10 x 50mm if the 6x is not enough for your kneads.
The eye relief on the Nikon is 4” and it doesn't change compared to the Leupold which will change depending on the power from 3.7” to 4.2”.
When I was hunting last season I was very impressed how the EURO performed under low light conditions but I’m curious to see how the Nikon performs for this season coming up.