It all depends on how you posted the comment.
If you posted it manually, it makes no difference whether the ratings are from different IPs. It will go to the top.
If you posted automatically, you need a new IP for every single rating, otherwise it will won't go to the top.
Keep in mind that no matter what if you overdue the ratings on a single IP they will remove all ratings from that IP. I did this last night and rated 10 manual comments with about 300 ratings all in all from the same IP. The comments are still there but all of the ratings got removed. (The actual thumbs ups got removed, I'm not just talking about its position)
This is incorrect.
I had about 50 comments posted manually. Then I proceeded to rate them with YTA with 90 youtubes with about 40 proxies tied up into them. All ratings were still removed the following day. Not only that, but right after the update the comments that were voted in, had all rates next to them and only about 5 of them went into a high rated box at that moment. The next day these same 5 comments weren't there anymore.