Sorry not to be specific the first time. By "half", the watermark is never fully square on the stamp because the crown and CA together are more widely spaced apart in this watermark type:

So only the crown
OR the "CA" appears on a single small-size stamp. This image was taken from a large-size stamp.
Note that if you reverse the parts, it looks like a normal Crown CA watermark sideways except that the crown and "CA" parts are always split over two small-size stamps. SG shows "CA" as having taller narrower letters than on the typical upright Crown CA watermark. That seems to be true much of the time for this watermark but is not so on the example shown.
SG lists the color of #1 as blue-green. Just checking around I found:
http://stampsjournal.com/labuan/labuan-stamps/ which shows the difference quite well, in my opinion.