in NSW generally excludes garage, front porch and alfresco and includes inside rooms and i include thickness of all the walls and try to avoid coming too close to the 50%

Maybe this can help. It reads that all buildings are part of the ratio.

https://data.aurin.org.au/dataset/nsw-govt-dpe-nsw-floor-space-ratio-2016-na

or this

https://www.planning.nsw.gov.au/Assess-and-Regulate/Development-Assessment/Your-guide-to-the-DA-process/Getting-started/The-planning-system

FSR generally excludes areas that are open or the wall is less than 1400mm high. It is defined in your council LEP and should say something like:

site coverage means the proportion of a site area covered by buildings. However, the following are not included for the purpose of calculating site coverage—
(a) any basement,
(b) any part of an awning that is outside the outer walls of a building and that adjoins the street frontage or other site boundary,
(c) any eaves,
(d) unenclosed balconies, decks, pergolas and the like.

If you site coverage is a control within the Development Control Plan (DCP), it can generally be varied with good justification and as long as it meets the objectives.