Seat tube angle help!

Hi got a new bike recently, the top tube length and the stem length are the same as my old bike as well as the saddle to bar drop but it is far less comfortable. Now the new bike has a seat tube angle of 74 degrees, the old one 73. It seems obvious the steeper angle of the new bike would essentially reduce the top tube length by 1cm as the saddle is pushed forward compared to the old bike with a 73 degree seat tube angle. Meaning to get the same reach one both I would need a 10mm longer stem on the new bike. But a paragraph on Sheldon Brown has confused me greatly;

"Generally, each degree of difference corresponds to about a centimeter of top tube length. Thus, frame "A" with a 58 cm top tube and a 72 ° seat angle can give the same riding position as frame "B" with a 57 cm top tube and a 73 ° seat angle. This presumes that the saddle would be slid 1 cm farther forward on the seatpost of the frame "A." http://sheldonbrown.com/frame-sizing.html

I think I am confused about the last sentence, surly the saddle on frame "A" would have to be pushed 2cm further. 1cm for the the steeper seat tube angle and one 1cm for the shorter top tube.

Anyway what I'm basically asking is if you have two frames with the same top tube length, one with a 73 degree seat tube angle and one with a 74 degree angle will the latter essentially have a top tube which is a centimetre shorter in comparison to the frame with the 73 degree angle?

No its the other way around.
The 74 degree frame will require you to reach 1cm more if you have the saddle in the same place relative to bb as the saddle will be pushed back 1cm more than with the 73 degree frame. In other words you will need a shorter stem by 1cm to achieve the same reach as your old frame.

ah ok thanks for that, really don't understand though still surly a steeper angle will result in a steeper seat tube? Meaning the saddle will be more forward?

I think I'm getting confused with how the seat tube angle is actually measured and the difference between a higher and a lower degree...

right think i understand this now, these comparisons are at with the saddle at the position over the bb...

Make a drawing - that should help you visualise it.

@Lukeyp

@edscoble posted a neat gif, i thought on the stack and reach thread but i can't find the gif

Top tube length, seat tube angle, and bicycle geometry. by jimmythefly, on Flickr got it now