The important thing is to remember that ice doesn't always form up the same length or thickness. What is one year (maybe when bolted) a blank section with no ice and no gear placement potential, might have ice several feet thick and solidly attached another, fatter year. But I must say that placing bolts in places where the ice is usually solid and protectable (like where you could presumably get a screw in while drilling that bolt) sounds kind of dumb, not to mention expensive for the first ascentionist.