How does structure feature spawning work?

can someone help me understand how placing a feature using a jigsaw block work? I've got this jigsaw placing dripleaves via a feature but I'm finding it hard to control how features are placed.
So what I kinda understand is that the referenced template pool calls the placed_feature. This then finds a bunch of places that the configued_feature will attempt to be placed.
So in my example how I'm imagining the placed_feature working:

it creates 225 positions where the feature can be placed (where exactly would these be? At the block above the relevant jigsaw block?)
it then moves them randomly 4 blocks in the x and z axes and 15 blocks in the y axis resulting in 225 positions randomly spread across a 7x29x7 rectangle centred on the block above the jigsaw block.
These positions are now moved downward block by block up to 32 times and if they encounter a block with the "type" of "solid" they stop (stop on the block or directly above it?).
I'm guessing it then tries to place the configured feature on every one of the resulting positions

The configured feature I'm much less sure how it works.

im guessing each type kindof had differnt ways it works and you can configure it.
For vegetation_patch, what does depth, extra_bottom_block_chance and extra_edge_column_chance do?
The ground_state just changes the block directly below the feature to a specifc block?
replaceable is what can be replaced by the feature.
not really sure how "surface":"floor" comes into it since it's already on the floor
vegetation chance is the chance that vegetation will spawn on each block of the patch
vegetation feature is what is places
vertical range and xz radius, do these determine how far the patch can extend?

So as I undersatand there should be dripleaves basically everywhere in a  7x29x7 cube but there aren't.