Quench
black arrow above same 1 3/4" as flat top

red arrows direction of
combustion on quench
black arrow above  1 3/4"

red arrows direction of
combustion on quench
Quench on  a flat top has as much to do with direction as it does with area.
Distance of quench dictates speed both horizontally and vertically.
On a flat top you have much more speed in the middle of the piston than you do at the middle of the
valve relief.
The vertical quench on a flat top is important to attain speed and direction.
Since on a flat top, combustion is located more on one side, reducing combustion area, it is important
to have the vertical quench as close as possible without the piston having contact with the head to get
a good mixture of air and fuel without having lean spots
The greater the piston to wall clearance in conjunction with bore size and pin location, the more rock
there is on combustion, thus a greater vertical quench distance is needed.
A 4" bore SBC with .004 piston to wall and a 1.250 pin location may only need about .030 vertical
quench but a 455 Buick 4.350  with .005 -.006 piston to wall, a 6.800 rod and 1.795 pin location needs
about .040-045 depending on RPM. Aluminum rods require more because of expansion in length.

Now when we use a dish piston, the quench area and horizontal distance is greatly reduced and would
not have the effect of a close quench as with a flat top.
That being said with a dish piston we have the entire area above the piston for combustion.
Also note that as the piston is on the compression stroke the direction of the mixture
is towards the
center and the mixture ends up in a swirl in the direction of the arrows.
Why a dish piston does not need a tight quench