Truncation to be used for Open Space Determination?

Does anyone have any experience with the inclusion or exclusion of the truncation area in the calculation for open space? I.e., can you have a bigger house due to the truncation?

We have a truncation on our block (18 m^2 total) and we are pushing the limit on open space with our house design (mostly due to me having the alfresco with only 1 open side therefore it doesn’t count as open space).
If you consider our actual block we are 3 m^2 over the limit, however if you include the truncation we are 7m^2 under the allowable limit.
I am discussing with the designer and he is going to discuss with council, but I wanted to run it by people here to see if anyone has had any experience.

With the site area measurement (Figure 1a in the R Codes) the truncation area may be included in the site area. That makes sense and I’ve seen it used to have lots smaller than the R code would otherwise allow.
My thinking is that if you add the truncation to the lot size, you should also use the ‘increased’ lot size in your calculation of open space %.

There is potentially some ambiguity in the wording of the definitions.
The definition of Open Space (“Generally that area of a lot not occupied by any building…”) refers to a “lot” rather than the “Site Area” (which is referenced in Figure 1A).
Our block was a built strata duplex (built in the 70’s) and has had a survey strata division in recent years. The definition for ‘Survey Strata’ is “A lot and associated common property as shown on a registered survey strata plan prepared in accordance with section 4(1b) of the Strata Titles Act 1985, as amended.”