The best, if rather unorthodox, solution I found so far is the HK-3. It doubles as an enlarged focusing collar to make focusing easier as well.
The HN-14 is just ridiculously large and ineffective. Its main impact is drawing undue attention to the lens. The HN-1 is better and less conspicuous, but not very efficient either. Plus even with a slim filter on the lens, it will vignette. One could say similar for the HK-3 if shielding from side light was the only concern, but in this case there is no vignetting from filters due to the manner in which the hood is seated.
By the way, HK-6 will not fit unless one always uses a filter, and even then, is easily lost.
Thus basically one can forego any hood and rely on the old hand technique instead. However, the front element of the 20/4 despite rather small, is not well protected and without a lens hood can easily be scratched in the field. Enter the HK-3 to the rescue.