ok, rbernie, looks like, as you're coming forward on 1.65 power, the black edges don't start to creep in from the sides until right about 4" of ER; *maybe* 4.25". So you've got roughly 4-12" or more of ER on this setting.
On 5 power, doesn't start to black out on the front end until 3.5" or closer. So you've got roughly 3.5-5.5" of ER on this setting. Not nearly as much going backward, so I misspoke when I said 6" easily. It's 5" EASILY, and closer to 5.25 or 5.5". You can still USE it farther back than that, but you'll just have the center view with black edges.
Good luck and report back!