Regarding getting lower - I was down on the ground but I was on the bank at the edge of the pond/lake so i was about 2 to 3 feet above the water surface. The duck was out far enough so that I felt the angle was reduced enough to be good. I guess it could have been better.
Regarding the whites - I felt I had pushed the white close to the limit without crossing over to "hot". But maybe not. Probably should have gone to -2/3 EV but the histogram looked good at -1/3 and I was trying to expose to the right.
Great find, details and I also like the half-raised crest. The whites look good here, you could selectively tone them down to see if you get more details this way.