As mentioned in this "trimmed hedge" related thread:
"The Edge Boundary Checking
mode is not meant to "slice" the geometry, it's removing elements within one item that are "based out of area used for distribution". So, if there are any "overhanging faces" under one element, these will be fully removed or not, depending if the element is based inside/outside of the distribution area.
It behaves like grass blades in nature - if there is a space enough to growth from, the grass blade vegetate and later could overhang that area. Additionally, this way it doesn't affect overall performance (as massive geometry slicing would require huge additional resources).
As mentioned above, there is no "physical cut" performed while using the Edge Boundary Checking
mode (as this would be extremely resource demanding). This "trimmed part" is treated by the render engine as a kind of "Matte object" internally (this way render engine ignores it for its calculations)."
For both the Lawns
presets you will see there are two versions for each type, one with a (detail) suffix and another with a (large) suffix. Unless you're filling a large area, I'd pick the detail ones.
Also, please feel free to send us
your scene (ideally a simplified version of it) and we'll check it here. Thanks in advance.