Welcome to the forum. Plenty of Perth people here. There’s a thread too:
https://forum.honeyflow.com/t/perth-wa-au-flowhives-and-honey-flow/
For what it’s worth, my local bee ware supplier sells hives with full vented tops:
https://www.beeequipmentaustralia.com.au/product/10-frame-base-boards-10-frame-roofs-bee-hive-beekeepers/
Perth had relatively mild winters and we can get away with this. I run a similar setup but with solid bottom board. My colony has dealt with this setup without any issues - through winter and summer.
The bees will build and propolise structures as they see fit. As a bee keeper we are just OCD and try to dictate this - hence managing ‘bee space’ is important.