What Don said and "be careful"!
The manufacturer spec is often at standard ride height (swing arm might be angled down a little) and they often use the most forward axle position in deference to strange tax laws in other countries. When you lower the bike (before adding onto the swing arm length) you may find the maximum rear axle position remarkably close to the "spec + 10%" number.
I caught myself screwing this up, one year, thankfully in time to fix it. It was just a bummer cutting and welding on the swing arm twice, to get it right....once.