I did have another thought about mounting on the handle top.
First, let's assume that the bullet comes out of the barrel, and goes straight, unaffected by gravity.
Moreover, let's say the scope optical axis is perfectly parallel with the rifle bore.
Now to exaggerate wildly, let's put the scope up three feet in the air.
Now, I can see two problems.
1. You can't put your cheek on the stock while sighting through the optic.
2. The bullet will impact three feet below what the scope indicates.
You would need to tip the scope down each time, after you determined the distance of a particular target. That is, the scope line would have to intercept the barrel line, right where the target was located.
The situation would improve as you lowered the scope down toward the barrel.
I apologize for not knowing the formal name for this condition.