Thanks Rick and Region2, that is helpful. That tip sheet answered my question: "eBay will accept just the next increment over the previous bidder's max. This is why it is safe for you to put in the absolute maximum you're willing to bid. Remember that eBay doesn't show a bidder's max, just the next increment needed over the previous bidder. - Your snipe bid will jump to a seller's reserve. This would happen if you bid directly on eBay too."
I didn't understand how Sniper could incrementally bid up beyond your opponent's maximum proxy in the short time available. But that makes sense...Sniper puts in your max bid, and Ebay automatically jumps to one increment above your opponent.
Game on! I'll post how it went tomorrow.