usually, percentages in a report, when applying a breakdown, refer to the item that is broken down from.
Example: Device Type Report > Break down "Tablet" 100 Visits with "channel" > i.e. channel1 has 10 Visits, so 10% will be shown
When I break down a mapped item (Classification Rule Builder / SAINT), the percentages refer to the Total Volume. I.e. if the Total Volume is 10000 Visits, but I break down the item of 100 Visits and the first item of breakdown (variable2) is 10 Visits, it shows 0,1%.