Hmm... This whole post may sound cynical, but... I'd have to say that maybe, like you suspect, you're not the single handicap that you think you are/wonder if you really are. If you're playing from tees that are too close (especially for an 8.5), then you're not getting a true accounting of your game.
To me, part of golf (and the difficulty of it) is coping with the length of a given hole. And, along with the actual raw yardage, you have to cope with the hazards that, most likely, have been placed where they are to demand different shots. Sometimes a lot of carry is needed to clear something off the tee. (If you don't clear it off the tee, then you're required to maybe hit a longer or more accurate iron/wood than you would have prefered, making things yet more difficult.) To me, that's part of golf.
I looked at that par 3 that played 300 yards one of the days at Oakmont this year, and I thought it was insane. But, then again, I'm not a pro. When you consider that pros probably ought to be able to hit the ball 300 yards, then it's not so insane. Obviously there is thought to be SOME relationship between overall ability (which we measure with indexes) and ability to hit the ball a good distance.
You say your short game is great, but your lack of distance hurts you badly? Then I think you need to work on your long game, because your 8.5 index certainly isn't telling the whole story. Just like I shouldn't be allowed to not putt when I reach the green, you shouldn't be allowed to start at tees that are much closer to make up for your shortcomings (pun moderately intended).

If you are a senior, or a woman, then closer tees are provided as compensation for generalized physical limitations associated with those categories of player (despite the fact that there are probably plenty of seniors and women out there that could drive me off the course). If you don't fall into one of those categories, then, well, I think you should be playing from the middle (typically white around here) tees. I think you'll find that scores from there more accurately portray how your overall golf game is. If your index goes up a lot, that's just an indication that you need a lot of work on your long game.
I just played with a buddy of mine who simply can't keep a wood of any kind on the course. He has to hit 3-iron off of each tee. And, even when he does that, the ball MAY go 120 on a good shot. But the ball doesn't go 120 because of his equipment -- it goes that distance because his swing is a mess (and he knows it). He putts fine, and his short game is decent. But you'd never mistake him for a "good golfer." Should he play from closer tees? No -- he should get help with/work on his game. In the meantime, he simply won't score well. When he starts putting a good swing on the ball, the ball WILL go far.
Golf often requires that you be able to hit the ball some relatively far distances. Hitting the ball ACCURATELY with a longer is usually more difficult than with a shorter club. And that's golf. It's why we complain that our putting was great, but we couldn't get off the tee. Or that as the driver caught fire, the irons went to crap. It requires mental and physical ability, and a ton of practice for most people.
I think you need to back up to the tees that you really ought to be playing, re-evaluate your game, and let the higher scores come initially. Length off the tee is part of the game, and a part that you might simply need to work on a whole lot more.
Good luck! This game is tough -- but it's the best.
/< / /2 /<
PS -- I've often looked at Long Drive tournaments on tv and wondered if some of those guys are ALSO good golfers. We know they can hit a ball a mile, but can they hit greens in regulation? Can they put? Can they get out of the sand well? Right now, I'd say that you can't be sure that you're an 8.5 until you can cope with the length of a given course from the "appropriate" tee box.