Tuesday's third-round tie at the Kiyan Price Foundation Stadium saw Benitez's men crash out on penalties after a 2-2 draw.
Everton, who were beaten 3-0 at Aston Villa in the Premier League last weekend, twice trailed to Charlie Austin headers, with Lucas Digne and Andros Townsend netting equalisers.
In the subsequent shoot-out, Jimmy Dunne converted the winning penalty after Tom Davies' kick had been saved by Seny Dieng as QPR triumphed 8-7.
Benitez told evertontv: "The most difficult thing to improve, normally, is in attack because it depends on the quality of players, but we are creating chances, so I am sure we will score goals.
"But in defence we have to be more aware of what is going on around and be sure we defend as a team, and then (if) we are strong enough in defence, that will give you the possibility to win games.
"You have to build the momentum from a solid team. At the same time, we are creating chances, so we have to find this balance that still we cannot find."
Everton – unbeaten with 10 points from a possible 12 prior to the Villa game – host Norwich on Saturday in their next league fixture.
While Digne and Andre Gomes will have calf issues assessed ahead of that contest, it certainly appears there will be no involvement for James Rodriguez, who has travelled to Qatar to discuss a move away from the club.
It was understood Rodriguez was to have talks with Al-Rayyan, and according to the Liverpool Echo, Benitez said of the Colombia international on Tuesday: "To be fair, I don't have too much information.
"I know he is already there (Qatar). Maybe in the next couple of days we will have some more information."
When asked about the prospect of Rodriguez being involved in Everton's next game, Benitez said: "Very difficult."
QPR boss Mark Warburton spoke up for the Carabao Cup in general following what he described as an "outstanding" tie.
Warburton told his club's official website: "I spoke to a couple of people and they said, 'you want to be in that thing?' I cannot for the life of me understand it.
"Anyone (at the stadium on Tuesday) would know the importance of going as far as you possibly can in every major competition. It's a magnificent tournament.
"We've got a Premier League scalp, a packed stadium, the fans were magnificent, getting behind the team, more belief in the team, they see what it means to the players that pull the jersey on. All the old cliches come out and there's a reason why they are old, they are around for a reason.
"You saw everything about a magnificent cup tie, a great stadium, the noise, the smell of the grass, the floodlights – outstanding, and that's why we play football."