FirstVisibleLine

If using FirstVisibleLine, it doesn't move to the line number specified, rather it moves to that count of lines. In other words, if I want the firstvisibleline to be line 50 and I have a collapsed region above line 50 that contains 20 lines, then FirstVisibleLine will actually move to line 70.

Question #1, can you change the behavior of FirstVisibleLine so that it uses the absolute line number instead of the relative line number?

Question #2, if not, what is the easiest way to get the relative line number from the absolute line number, so that I can pass that number to FirstVisibleLine?

Thanks.