You have some great cycling there. Gurgle maps puts you just NE of Adelaide. I watch the Tour Down Under every January, not so much for the racing but for the scenery. Marvellous countryside there.

Audax bikes in general make great commuters. One of mine is the Ribble Winter/Audax. Aluminum, but still an audax bike. And true to its name, it loves long rides as well.

There's nothing in the geo specs about the fork or "trail". My comments here are based on audax bikes in general.

I'd drop down a size to keep the stem in the 100 to 120 range. Audax bikes tend to have "low" trail. (See Trail and Its Effects at Spectrum Cycles.) A short stem is likely to exacerbate its effects on handling and make the bike feel all wonky.

Keep in mind too that the short reach bars have an effect here as well. It's not just a matter of manufacturers preferring the look of long stems as suggested by one poster above. Overall reach is the sum of effective top tube length, stem length AND handlebar reach. Short reach bars with a short stem is doubly an issue.

I like the way my low trail audax bike feels in commuting, especially on rough roads and the cobbles. That it wants to keep tracking straight ahead is a real boon on bumpy roads in traffic. But it took some getting used to--especially the cornering--since my other two bikes are high trail and neutral respectively.

For the record, I use a 100mm stem with 85mm reach bars. This is about the same as 70mm reach bars with a 120mm stem.

While there's plenty of room for personal preference, the general idea here is to place your hands between the axle and the contact patch--directly above the space we measure as "trail". You have a few cm to play with so it's not a precision thing, but provided reach is in the rider's comfortable range, most road bike riders prefer that's where their hands end up. Since the trail is in a fixed place--between the axle and the contact patch--once you have your hands above that, the only other thing you can change is top tube length.

This is why it's preferred to get the right top tube length to start with, rather than mess around with stems. Yeah a shorter stem may fix things relative to your shoulders or keep you from overstretching your back, but at the same time it may pull your hands too far back behind the axle. This throws off handling and ride feel.