Question about [stat-RHI ]

Here is a simple object.
This object has 20 triangle polygon.
but in stat - RHI in UE4, I can’t find a number ‘20’.
Also, I can’t find the count 12(only polygons seen in real time through the viewport).

All I can see is some huge numbers.

why?
And how can I know the number of polygons on the screen as I initially intended?