Hi Ketch, I suspect the problem may be the thickness of your coping sled. From the photos, it looks like the collet can reach at least the bottom of the router base, if not actually protrude through it. The underside of the table is routered out to accommodate the quickmount plate, which is itself sheet metal, not very thick. Your photo shows the bit clearing the table surface, but obviously not the coping sled.
Unfortunately I have zero experience with that type of router - they are uncommon this side of the Atlantic. But I would be surprised if its intended range of movement is too small to allow the use of the bit you show in the picture. Perhaps somebody who uses a similar Craftman can advise you on what may be restricting travel - the use of the extender is introducing a bunch of new problems, and is preferably avoided.
You might have to do without the coping sled. I made one, but abandoned it. Over the years, members have described various alternatives. I often just use a substantial scrap block, with two edges at right angles to each other: one edge bears against the fence, the other supports the workpiece. The block needs to be large enough to keep your fingers well away from the bit.