If 10% of the volume of water is lost during the 10 minute boil (assume no solids are lost during the boil) ...
That calculation caught my eye. A ten minute boil is a long time for a small amount of liquid. I brought a quart of water to a boil in a two-quart saucepan, uncovered the pan, and set the timer, then turned off the flame and poured out the water as soon as ten minutes were reached. The water had lost 50% of its volume.
Obviously, there are easy fixes: add preboiled water to restore the volume. Start with more than a quart of water. Cover the pan for part of the boil. Palmer recommends, "Put the lid on the pan for the last couple minutes" -- I do that anyway, to steam down any wort crystals and to kill the bugs -- and that would also help reduce loss.
But the key is to know what your target OG should be for your starter and focus on that, and I can honestly say I haven't been doing that for starters (why, I don't know, since I am almost obsessive about hitting my OG for my beer).