total items remaining doesn't accurately reflect state of indexer

When building an index over an existing data set, I see that the items remaining statistic goes down to 0 while the index is still in pending for a long time and the disk size still growing.

Is there a way to tie things a bit more closely together so that items remaining is more accurate? Or is there something else to monitor to know when an index might be getting close to actual completion and moving to online?