I am sure this is in here somewhere, but I have had little luck on specifics.

2 questions.

1, what is the real difference between HD and 16:9 when using the frame guides ? When I'm in HD - and I set the LCD on cam to 16:9 frame guide with a 4:3 safe, the lines don't match the external monitors. There is more area on the sides in the external monitors - and when I am framing for 4:3, the director using the external monitors frame lines will see that he has more room to work with when I say I am at the edge. I know monitors produce there own frame lines, but is it an HD thing that causes this? because there is no way to select HD frame guides with 4:3 safe.

2, Why HD vs. 16:9 anyway? what are the differences in the 2 choices, other than the obvious... "more frame at 16:9"
Any help would be appreciated