[Freesurfer] Frontal signal drop out

Dear Experts,

Sorry if this is a repost, but I was not sure it got posted.

I have a few subjects that I want to salvage and use where there appears to be significant signal inhomogeniety in the last few frontal slices (see T1.mgz in attached figure 1). Despite the use of control points (placed with careful adjustments of windowing parameters), I still can't encompass all of the the gyri right at the front (see brainmask.mgz coronal slice in figure 2). I would really appreciate some advice on how to proceed from here. Is placing white matter voxels in wm.mgz a possible solution ? Or is there another solution ?

Thanks.

M