I too own an Eden 600 - knees in the beams have been always been an issue (front and back beam only). As we usually also have the side extension on - did think it was partially due to extra weight on top of the tent.
During torrential rain the back beam would collapse.
Even sent the tent back to Attwoolls for them to pitch and sort out the issue.
They reported no issue, but stated should inflate to 8psi (we have found that day 2 onwards this settles back to 7psi anyway.)
So have lived with the issue most of the year and given that we have kids running around - spending time finessing the beams was not a high priority.
Our last camp of the year was August bank Holiday we packed the tent down, not completely bone dry, so when the kids started back a school we erected the tent to completely dry out and to play with the beams.
I can report that by partial inflation of the beam in question and unzipping the outer sleeve we were able to finally get rid of the knees (on a flat field), they were twisted / kinked in the sleeve.
Also a point of note is check how the beams sit on the velcro pads as this can be a variable when packing down.
Hope this helps.
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Update! Ok so we had a dry day today here. I got the old faithful out on the back lawn and put her up. Took out both the front and rear airbeams from there outer sleeves then again took the inner tube out from its sleeve and examined the beams. They didn't seem to be folded much at the ends but anyway after I reinflated the beams once back in the tent I am pleased to report NO KINKS n the front or rear beams. So whatever I did it seemed to do the trick which I am very pleased about as the kinks in the airbeams were annoying. Took the time to snip off a few of the random threads hanging about in the tent ceiling too whilst I was at it! Looking forward to campimg next year now and I think 2 weeks in Cornwall is on the cards, somewhere fairly relaxed and low key maybe. Thanks again for your advice on this problem.