McCoist's out-of-sorts side conceded three goals at home to part-time SPFL League One rivals Stenhousemuir.
It was not the first time in recent weeks the runaway leaders have looked fragile at the back in home games.
They let in two against Arbroath last month and were lucky to only give one away against Brechin City the week after that.
The Light Blues manager fears his side is being caught out by visiting teams who are sitting deep and hitting them on the break.
He said: "The fact we lost three goals was the most disappointing thing. When you score three goals in a home game you expect to win. It was a disappointment.
"I think that perhaps teams are counter attacking us well at Ibrox. At their own grounds they are under more pressure to attack us with it being their home fixture.
"We are possibly getting caught out of position when we are searching for goals at home. It is something we will have to look at."
Meanwhile, McCoist has claimed referee Greg Aitken got two contentious penalty decisions wrong in the 3-3 draw with Stenhousemuir at the weekend.
Aitken booked David Templeton for diving in the first half when he went down in the visitors' area and then penalised Emilson Cribari for a pull on David Rowson in the second half.
McCoist said: "I thought the referee got both of them wrong. It was harsh not to get the penalty. It was harsher for Temps to get booked for a crime we felt he didn't commit.
"The foul was given for Cribari tugging somebody. Having had a look at it I would have to say he is one of very, very few referees who would give that award."
Meanwhile, McCoist has revealed he is not expecting Rangers right- back Sebastien Faure, who was stretchered off in the first half, to be out of action for long.
He said: "He is fine. He went to hospital for an x-ray and is fine. He has just got a really sore one down his shin and his ankle.
"But, thankfully, there were no breaks, no fracture and, as sore as it is, he will be absolutely fine."