Voltage drop when transformer on site

[electricaljc]

I've got what may be a stupid question but the only answer that I can come up with is 'because it says so in AS 3000', is there a reason why you only get 5% voltage drop when your transformer is on the site but not dedicated to the site? To me, the physics would suggest that it should be no different to being dedicated and getting 7% so I'm needing someone to break it down. Thanks in advance.