From what I can see in both the Takeoff and Custom Takeoff Reports, the Topsoil Strip will report by AOI and as Erik states it does not report Remaining Area at all as far as I can tell - It will report the AOI Areas but not the Total strip. For example I created an OG Surface that covered the entire site, I then defined the AOIs for 2 Areas inside the site and there are gaps between them. When I report the Topsoil Strip using the AOIs I get the Topsoil quantities of AOI 1 and of AOI 2 but not the total Topsoil strip defined over the entire area. If I then add the OG boundary that I used to create the topsoil strip over the entire site as a third AOI I get the total of Soil Strip over the whole site in that AOI and I get the two parts in the other two AOIs - but that doubles up the quantities in the areas where the AOI Overlaps occur - You would need to subtract the AOI 1 and 2 from the full area AOI to get the remaining area Topsoil Strip quantities.
So based on this I dont know what the Report Remaining Area is doing in the case of Topsoil Strip as in my view it should be the Total Strip - AOI 1 - AOI 2 quantity.
I will report this in as a defect
Alan