The Cottagers have been one of the most entertaining teams in the Premier League this season, scoring 24 goals in 11 matches.
At the other end, though, Fulham have conceded 19 goals and been involved in a number of high-scoring draws, including last weekend's 3-3 at Arsenal.
"If you see the first goal, for example, against Arsenal it was a set play again," Jol said, speaking ahead of Sunday's clash with Sunderland.
"Of course you don't want that and we have to come up with something better, you know?
"If you see, for example, Reading, Southampton, Arsenal - 60 or 70 per cent of these goals were set plays, corners and free-kicks.
"We still scored more goals from set plays than we conceded but it is a little worrying and we spoke about it.
"We knew exactly what Arsenal were doing but they still scored, so we have to be a bit tougher.
"We have to put that right because it is awful if you score three goals away from home at Reading or Arsenal and you still don't win. It is frustrating."
Whites captain Brede Hangeland this week suggested Jol is looking to add to his defensive options with international team-mate Forren.
The Molde centre-back is attracting reported interest from a number of high-profile European clubs but Jol believes any Fulham move has been ended by Hangeland's comments.
"Most of the time if I ask for players from Norway they're not that positive," the Dutchman said of his chats with Hangeland and countryman John Arne Riise.
"With this boy they were positive but that is the only thing I did.
"I don't want to talk about targets, you know? This is more private.
"It was nice that Brede said something nice about his team-mate but that is not normally what you want.
"You want to keep this information for yourself, but he did well. He was open and honest so now we probably have to switch to another target."
One of Jol's most successful signings in his short time at the Fulham helm has been Pavel Pogrebnyak, who impressed after joining the club in late January.
The Russia international rejected an extended stay at Craven Cottage to join Reading in the summer and insists he had no regrets about the move despite his new side being in the bottom three.
Jol has seen a number of players leave since taking over and again reiterated today [Friday] that the grass is not always greener on the other side.
"I couldn't come up last year with a lot of players that have done better away from Fulham so this is a good club for most of these players," he said.
"They do well here and, for example, Dimitar Berbatov maybe six months ago would never have thought about the fact he would play for Fulham.
"He is here now, he is doing well, he is happy so maybe that is a good phrase for these kind of situations, that the grass is not always greener.
"But he had to make a decision and I don't think the Pog should look back. He will do his best for them because he did very well for us."
Pogrebnyak's time at Fulham may have ended but Jol's stay at the club will be extended once the paperwork is complete.
"I was quite clear they had an option," he said. "I had two years plus a one-year option for them and they took that option so that makes it three years.
"Formally they have to send a letter and I think they will do that."