"Primarily location," he said. "It was better against the White Sox and it was alright against Detroit, but especially in key situations, I need to locate better."
He noted Tigers catcher Alex Avila's pair of run-scoring hits on Saturday as an example.
"I made a couple of pitches to him that needed to be better," Collmenter said. "And if they were, it's a different ballgame."
Collmenter hasn't walked more than three batters in any of his nine starts this year, has only walked three once and has walked fewer than two in five starts.
But he's found that it's as much about where he throws the ball around the strike zone as when.
"A lot of guys seem to be pretty aggressive early," Collmenter said. "Just seeing that is important for me to be able to throw all of my off-speed pitches for strikes.
"Then you can throw something other than the fastball first pitch and other times you'll get them to take because they're looking for that first fastball."