That's an issue I'm familiar with. I don't have it, but one of my close friends and riding buddies has had it for years. I finally got him to adopt a more stretched out position with slammed stem, which helped him a lot. He now has that position on all his bikes. Try it. First get balance right with saddle position, so little weight on hands. Standard is to pedal down the road and be able to lift both hands off the bars without sliding forward on the level saddle. Next, adopt a stem length that allows you to have your elbows forward of your knees when on the hoods with horizontal forearms. Then lower the stem as much as your flexibility will allow and work on that, which you are certainly already doing.
Having done all that, be sure your pelvis is rolled forward on the saddle so that your back is as straight as you can get it. You want to bend at the hips more than in the lumbar spine.
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