The Amazon Kindle Publishing Guidelines recommend putting in a "start reading" location on page 15 of version 1.6.
Unfortunately, they don't actually tell you how to accomplish this, and it's left as an exercise for the e-book creator to look it up in the old Mobipocket Developer Centre's info on "
Guide items".
Also, I agree that your problem may be with the underscored id. In XML it doesn't matter any more, but Mobi is basically a modified HTML 3.2, which is supposed to be pretty strict about id tokens only starting with certain characters (can't even use numbers), so perhaps you might like to try changing that.
I think that if it doesn't find anything valid, it may default to the first non-cover "page". Although this hypothesis is shot if it's skipping past a bunch of copyright info to hit the acknowledgments you mention.