Why doing overunder without GROW increases HPN/FPN values?

Hi, 

I have a rules file, where we are trying find all polygons on say M1. Also, we want to merge polygons which are within a certain distance. So, we have the following in rules file (rule.pvl):

// get all M1 outside SRAM

active_non_array_0 = NOT M1 SRAM_MARKER

// Merge all polygons within 100 nm

active_0 = SIZE active_non_array_0 OVERUNDER BY 0.100

After the above overunder step, the FPN and HPN count are more than from generation of active_non_array_0. However, if I add a grow step in between the two rules above:

active_non_array_0 = NOT M1 SRAM_MARKER

active_temp01 = GROW active_non_array_0 -top 0.2 -bottom 0.2 -right 0.2 -left 0.2 -sequential

active_0 = SIZE active_temp01 OVERUNDER BY 0.100

then HPN/FPN number decreases significantly. 

What is happening in the first case, why does FPN number increase? Also, does the number inside paranthesis below, give us the total number of polygons in the output? 

 Total DRC Results                 : 35788023 (2357970903) 

Is there a way to get the total number of vertices ? 

Thanks

Srivaths