Improving a walkforward test

I have a walkforward test over a 12 year timeframe with In Sample (training) periods of 4 years, followed by Out of Sample periods of 1 year. The results and equity curve are quite good with the exception of 1 year. I'd like to improve that year to be positive also. Just wonder what some experienced walkforward users do for this situation. Possibilities are to change the length of the IS and OOS periods, change the trading system itself or change some other walkforward setting. K-Ratio is used as the optimization target and I've found K-Ratio to be very good in finding smooth equity curves.

Suggestions appreciated.