There's no hard and fast precedent for this. Some applications call for higher EPA amounts compared to DHA, and others vise-versa.
Supplementing DHA, on top of your fish oil to maintain 1:1 could be seen as over-thinking the whole thing. If that makes you happy, and makes you feel good, then more power to you. Otherwise, just take a high quality fish oil/cod liver oil, and don't worry. :-)