Garage setback, R20, Perth query

Hello All! I want to build a new two car garage on my R20 block. Code tells me front boundary setback is 6m for R20, but 4.5m for a garage. Does this mean I can build the garage 1.5m into the primary street setback (i.e. at 4.5m back from the front boundary)?
Location is City of Stirling.
Also, my neighbor has a zero lot wall that starts 4.7m back from the boundary. It's an old house so would have been approved decades ago. Would I be allowed to build up against his zero lot wall?
I will engage a professional in time. Just want to understand options at this stage.
If it makes any difference the house is well back on the block (over 15m back).

 

Have you read the local planning scheme and policies?