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Your reasoning about the northerly location is correct at the middle of the day. At the end of the day your viewing location has rotated roughly 90 degrees which is a whole other configuration.
In the middle of the day, the tilt of the earth (in summer, moves sun position southward), along with your tilt from your southerly position (you are tilted towards south, making the sun appear northwards) combine. From Perth, your tilt away from the sun is still larger than the Earth's tilt is bringing you towards it. But when the earth has rotated 90 degrees from that position, your tilt is perpendicular to the sun and has no effect.
The trick to visualizing any of this is to use models. Some folks can model 3D space effectively in their head, otherwise grab some sports balls.
Place a ball representing the sun off in the distance. To represent Earth, grab a basketball, which has conveniently marked poles, and place a dot on it to represent your location. Now put your left middle finger on the pole you decided was south and your right middle finger on the other pole. Hold your arms outstretched so Earth is between your eyes and the sun ball, left hand down, right hand up. The Earth's axis should be vertical and perpendicular to the sun - no tilt yet. The silhouette you can see around the Earth ball is experiencing sunset/sunrise. Spin the earth, left towards you until your dot comes around and is on the left silhouette. Your dot, and every point on the left side of the silhouette will have the sun ball to the west. If your dot moves north or south on the ball, the sun ball is still to the west.
Now push the south pole towards the sun and the north pole towards you. Note that from the perspective of your dot, the sun has moved southward. Something else happened too - from where your dot is, the surface of the earth started to fall away and exposed the sun more - your dot is no longer at sunset. Tilt the Earth in the opposite direction, to represent winter, and the earth rises up and blocks the dot's view of the sun - the day is already over. The Earth doesn't change it's tilt like that of course (at least not on short time frames), to more accurately represent winter, you should move to the opposite side of the sun ball without changing the tilt. The effect is the same, the north pole is towards the sun.
Edit: I didn't see Hugh's post before I started writing this, I think his pics show it clearly.
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