Re: A 143

No. Because you've interrupted the attempt to stand up before the character got out of the prone position, you cannot make them "more prone". And regardless of what you do with the AoO, the character has not used their action and can just stand up normally afterward.Knock-Downallows you to make a trip attempt, but it will always fail if the target is already prone.

Having already stood up doesnotprovoke attacks of opportunity. It's onlybeginningto try to stand up that makes you let your guard down.

A 144You follow the above rule for diagonal measurement, with just one exception:Diagonals

When measuring distance, the first diagonal counts as 1 square, the second counts as 2 squares, the third counts as 1, the fourth as 2, and so on.Since your question is about Large and Huge creatures, you simply follow the basic diagonal measurement rule.Note: Small and Medium creatures wielding reach weapons threaten all squares 10 feet (2 squares) away, even diagonally. (This is an exception to the rule that 2 squares of diagonal distance is measured as 15 feet.)