Everard, I have the AOE-BAM metal tripod adapter which works fine on 12x60s. Sounds like you have the plastic one - AOE-BAP. I suggest that you upgrade. My 20x80s have the central supporting bar. I have looked at those AOE 20x80s and wondered how well they can be supported without a bar.
http://www.aoe.com.au/binoculars_accessories.html
I've made a few attempts to see the phases of Venus, but haven't been successful. I think you'll need very good viewing conditions.