Parkinson's side lost only one of their first 10 league games following promotion in May before Wells, sold to Huddersfield for B£1.3million earlier this month, was sidelined for a month in the autumn due to an ankle ligament injury.
Bradford lost three and drew one of the four games Wells missed and then drew five of their next six league games. Then followed three losses and three more draws, the latest against Sheffield United at the weekend, to leave them in 13th place.
"We've had a period where we've played well and drawn a lot of games, but I don't think we've had the front two functioning as we would have liked," Parkinson told Press Association Sport.
"Ultimately in football the strikers are so important and we haven't had our front two playing as well over the last couple of months."
Huddersfield paid a club-record B£1.3million for Wells, while Parkinson moved swiftly to fill the void last week by signing Hull striker Aaron McLean, who made his debut at Bramall Lane.
"We need to get a front two on the pitch which the rest of the team has the belief in that we're going to score," Parkinson added.
"We did start the season exceptionally well and if you forget about the recent run and take an overall look at where we are, we'd probably say 'yes, that's not too bad.'
"The clubs we're competing with at this level, it's very tough, so obviously we want to do better, we want to start winning games and we're confident we'll do that."