The number of formal disciplinary investigations at Gwent and North Wales Police has almost doubled in two years.
Professor Colin Rogers, a policing expert, said the figures could show that public confidence was improving in the complaint process.
The figures show South Wales and Dyfed-Powys Police had fewer investigations between 2012 and 2014.
It comes as Gwent Police plans to hold its first ever public disciplinary hearing later.
The move is part of Home Office Home office plans for a 'more robust, independent and transparent' system.
Details were made public following freedom of information requests.
BBC Wales also asked for the outcome of the disciplinary investigations from each force.
Gwent and Dyfed Powys Police declined to provide the information.
South Wales Police pointed to other freedom of information requests on their website.
North Wales Police published the results of their investigations in full.
It includes staff dismissed for "using discriminatory language against members of the public", "drink driving off-duty" and having an "inappropriate relationship" with a victim of crime.
Colin Rogers, a professor of police sciences at the University of South Wales, said there had been distrust amongst some in the past, when police discretion "sometimes wasn't used correctly", but added things were changing.
"We've seen a drift into the police becoming a profession where that discretion is now, most of the time at least, used and delivered ethically and proportionately," said Prof Rogers.
"That coupled with the fact that there have been some high-profile media cases involving celebrities and so on, which probably means that people have more confidence in reporting such matters to the police.
"More people are prepared to complain because they realise it's their right to complain, and I think the police force itself is more susceptible to dealing with those complaints professionally.
"To my mind (the increase in investigations) is positive because it fits in with the whole idea of accountability and transparency by the police for the communities."
Inspectors said last year that the Gwent force had one of the lowest public confidence ratings in Wales and England, though it is understood those figures have since improved.
Gwent Police has been criticised for its response to domestic abuse in the past, and for the way in which it handled a complaint against an officer who had sex on duty in 2010.
But the number of complaints against the Gwent force remained stable in 2013/14, at a time when the Dyfed-Powys area saw a reduction.
South Wales and North Wales Police areas recorded an increase in complaints during the same period.
Simon Newport, the chairman of the North Wales Police Federation said that while public confidence in the complaints system has increased, he questioned aspects of the process. Mr Newport said complaints should be dealt with "in a timely fashion" and "malicious complaints" should not lead to officers suffering sickness and stress.
Dyfed-Powys Police Federation chairman Dai Gaskins said the figures were "good news" for the public and officers in his area, who "realise the standard that needs to be met".
Gwent Police Federation chairman Jeff Mapps declined to comment, while his South Wales counterpart Steve Trigg, said by "airing its dirty linen in public", confidence in police forces would increase.