Now, we navigate into unknown (and perhaps silly) territory. Now we do point level calculations of heights, and drop the new calculated points back into the point cloud as though it were a Z value. I don’t recommend this code as a practice– this is as much as me thinking aloud as anything Caveat emptor:

/*
First we explode the patches into points,
 and along the way grab the minimum value
for the patch, and the id
*/
WITH lraw AS (
	SELECT PC_Explode(pa) AS ex,  PC_PatchMin(pa, 'Z') AS min, id
	FROM test1
	),
/*
Calculate our height value ( Z - min ) 
*/
heights AS (
	SELECT PC_Get(ex, 'X') || ',' || PC_Get(ex, 'Y') || ',' -- grab X and Y
	|| PC_Get(ex, 'Z') - min				-- calculate height
	|| ',' ||
-- And return our remaining dimensions
	PC_Get(ex, 'Intensity') || ',' || PC_Get(ex, 'ReturnNumber') || ',' || PC_Get(ex, 'NumberOfReturns') || ',' ||
	PC_Get(ex, 'ScanDirectionFlag') || ',' || PC_Get(ex, 'EdgeOfFlightLine') || ',' ||
	PC_Get(ex, 'Classification') || ',' || PC_Get(ex, 'ScanAngleRank') || ',' || PC_Get(ex, 'UserData') || ',' ||
	PC_Get(ex, 'PointSourceId') || ',' || PC_Get(ex, 'Time') || ',' || PC_Get(ex, 'PointID') || ',' || PC_Get(ex, 'BlockID')
	AS xyheight, id FROM lraw
	),
-- Now we can turn this aggregated text into an array and then a set of points
heightcloud AS (
	SELECT PC_MakePoint(1, string_to_array(xyheight, ',')::float8[]) pt, id FROM heights
	)
-- Finally, we bin the points back into patches
SELECT PC_Patch(pt) FROM heightcloud GROUP BY id / 20;