The Giallorossi lost 2-0 to last season's finalists and their performance was criticised by Ranieri for being too reactive and not positive enough.
"We were far more attacking last season, but tonight we waited for Bayern too much and were simply too passive," he said.
"I think that might also be because of the five goals we conceded at the weekend and so coming here against the vice-champions of Europe, it was a nervous occasion.
"Perhaps Bayern believed in the result more, plus they were helped by Thomas Muller's world-class goal. I was not disappointed with the side, but we do have to be a little more determined to make ourselves heard and support the strikers."
Ranieri admits it was a marked improvement on the 5-1 league loss to Cagliari on the weekend but still wants more from his charges.
"We did very well in defence, but didn't manage to develop our own attacking moves which are also built on passing," he added.
"It is a step forward from Cagliari, but we were still too timid and I wanted the side to be grittier.
"We have to keep working. We cannot support the trident right now, as to do that we need everyone to run, both in attack and defence.
"I saw we were a little more secure today and the team didn't split off into two chunks the way we did in Cagliari."