I have the FIA bar on my SV. I'm 5'8" so I don't have the problem you have, my head is safely below the top bar. I do have to remove the headrest when wearing a helmet as the headrest pushes my head forward and down, a very uncomfortable position for driving.
Caterham makes an adjustable helmet stop that clamps to the cross bars on the FIA bar. It does not come with padding so you have to do that yourself or outsource it.