Thanks a lot everyone. I think this was exactly the mistake that I
made, flying some type of hybrid between the two. The only wheel
landing I've experienced to date was when I went up to do inverted
spins a few weeks ago. I asked the instructor to demonstrate one, but
haven't done one myself. Therefore I should have reverted to the three
point attitude that I'm used to seeing. I think that subconsciously I
was trying to see if I could do a wheel landing. Or maybe I was
reverting back to the sight picture for a 172, which is probably
somewhere between the two attitudes in the SD. The three point
attitude seems more natural on the grass strip, whereas the flatter
approach of a wheel landing seems more natural on a hard top runway.
Maybe I just need a lot more practice. :-)

Dave