Looks like distance definitely has an impact on speed.
NBN say:
Your choice of speed and provider
To get the best nbn™ network experience, check your address and contact your preferred service provider about the options that are available to your premises.
Not all speeds greater than nbn™ 25 are available at all premises.
https://www.nbnco.com.au/learn-about-the-nbn/network-technology/fibre-to-the-nod...• At 100m, FTTN could deliver about 100Mbps
• At 500m, that drops to about 50Mbps
• At 1km, it drops to about 25Mbps
Lot of interesting info including how to determine your cable length to the node and maximum speed you can expect.
https://choice.community/t/with-nbn-distance-from-node-determines-speed/13707/19These are the factors that IINET say will impact the service:
Length of the copper line from your premises to the NBN node (typically in your street or a street nearby).
Weather conditions that may impact the copper.
Quality of copper line, including overall length, condition and joins.