While the hole for the HP in the head is over 90% scale the actual HP itself is less than 75% scale. This is really what's behind the stock HPs looking so out of proportion.  I'm guessing this is to save cost.

Original:
-Hole in head: 2-1/2"
-Grasp Opening Diameter:  1-5/8"

Home Depot:
-Hole in head: 2-5/16"
-Grasp Opening Diameter:  1-3/16"

Comparison:
-Hole in head:  0.93
-Grasp Opening Diameter:  0.73

Remove the exiting read HP:
Grind down the mounting holes flush to the dome:
Test the fit of the original HP: