You're welcome and for how tight to tighten the screw, mine was TIGHT when I opened it. I had to use some elbow grease to loosen it. I think the washer is intended to keep the screw from tightening too much and breaking the magnets. When I put my switch back together, I tightened it as tight as I could against the washer. I just opened it again and the magnets are not broken.
Also, remember you have a GLASS
tank on the AYS. It really should be in a holder, so whether it stands perfectly straight, shouldn't be an issue.

These can fall over easily and break the
tank. The ONLY way I would ever stand mine outside a PV holder is if it had a polycarbonate
tank on it. Not to lecture you or anything, because i know you are much more knowledgeable about these things than I am, but from the experience of one who has had her Zenesis tank broken, I HIGHLY recommend a stand for it...then you won't see it lean on the switch.
You may need the High resistance if you want to stand your Zenesis on its own without it leaning. I think it's just the nature of the magnet switch beast if you have it set to Medium or Low resistance to have it lean. OR, change the switch to a spring...like mac posted yesterday.