Honestly man, I have no idea why your ride height would change by tightening your chain. Are you making sure you have the recommended slack? Too tight will cause the chain to break. The owner's manual states the proper slop and always make sure you clean and lube the chain before you adjust it. Also, find the tightest point in the chain and make the adjustment from that point.
Taking all of the preload out of the rear spring may make it feel like it's lower, but you are mainly just increasing the sag of the bike. It will sit lower when you're on it, but you have no crippled the rear suspension. Never a good idea for a bike that is designed to handle well. There is an alternative, though.
Ebay has a lot of options for changing ride height. You can't use "Dogbones" on the rear shock. It's actually an aluminum plate design that replaces the stock stuff.
Sadly, the link is pricey, but it would do the trick. Here is the auction link
http://cgi.ebay.com/ebaymotors/Trium...item45ef45f3ab