Here's M46 with the foreground planetary nebula NGC 2438. The cluster fills the frame, making it not really stand out, but I used the RC8 rather than the ED80 to make sure NGC 2438 wasn't just a small dot.
I think you actually have the entire cluster near enough, width-wise. Trish and I compared your shot with a (very short) shot we took with the STL-11000M on the 20", which showed star-for-star identical framing, and a width of about 42 min arc. The cluster is catalogued as being 27 min arc across, and therefore you ought to have it all.
In our shot, we pushed the stars much less hard, nothing burned out, and the cluster stands out as being mostly blue-white stars against the generally more orange and much fainter background stars. Perhaps it's the limitation of what you can do with the DSLR (well done by the way), but just perhaps if you could do a slightly gentler rendition on the stars (and selectively enhance the PN if you need to), you'll see a bigger difference between cluster and background, and you'll find that you really do have all the cluster.
