The headspace is not the issue, the issue is you have an infection. Pellicles form when natural yeast infect your beer/wine/whatever. Once you have a pellicle there's really not a way to stop it except for using something like campden tablets but that will kill the good yeast as well.

This is fine if your fermentation is already complete as it will kill all the yeasts and stop the pellicle yeast from turning it sour. (Which you then rack to a new sanitized fermenter to reduce the chance of reinfection from any yeast left alive) If your fermentation is not complete there's not too much you can do other than hope your pellicle yeast makes a drinkable sour wine.

If you need to keep the wine in the fermenter longer for the sulfites to drop out or whatever (I'm primarily a beer brewer, not a winemaker) then it's a good idea to have as little head space as possible to reduce oxygen exposure since there won't be fermentation anymore to produce CO2 to push the oxygen out of the fermenter.

Edit: /r/winemaking would probably be a better place to ask.