Oh, I see you need to add another two posts to the equation! Let's think about post F then!
Let's say we want that post to be farther back, beyond post E.
What we'll do is find the middle section of the posts, horizontally. For this, we will trace a guide going through all the "X" we traced before (before we did this vertically, to draw the posts, we now do this horizontally, to follow the perspective and figure out the middle of our posts). Now we should know where the middle of our post E is.
The next thing is to make sure our perspective guides are going farther back, into the vanishing point. So we use a ruler to expand them (we already traced them before, going from top of post A to top of post E, and bottom of each, too). This is sorted out in the workbook.
What we'll do next is trace a line from the top of post D and through the middle of post E. But we wont stop there. We will carry on with that line until it touches our perspective guide from the bottom. That would be were the base of post F is located.
Now to find out where the top of post F is located, we trace a line from the bottom of post D, through the middle of post E and finishing when it touches the top perspective line.
Now we should have the top and bottom of post F figured out. We just need to connect those two with a vertical line!
We repeat the process with post G!
And in the end, we shuold have 5 new posts evenly paced and in perspective!
Was this clear? I hope it was of help! Let me know if I can make something clear!