The Italian deployed a back three in the 3-0 defeat to Premier League leaders Chelsea last weekend and reverted to a four-man defence for Sunday’s trip to Southampton.
However, Ranieri used a midfield diamond and saw his side slip to another 3-0 loss, and he held his hands up to take the blame.
“I think the last two matches I changed the shape to try to help my players to play better to find the right solution. But maybe I make mistakes,” he told Sky Sports.
“I was wrong against Chelsea with three at the back and also today when I wanted to play with the diamond.
“My players are familiar with the 4-4-1-1 and know the positions. I wanted to give something more, but I made mistakes.
“I think it’s much better to give them what they know very well.”
Ranieri replaced Nampalys Mendy with Marc Albrighton for the second half after his team went into the break 2-0 down, but he could not argue with the result.
He said: “We tried to change our shape. We tried to make a goal, maybe if we scored then we would have had a chance to maybe change the match.
“That’s no excuse. They won, they played better than us.”