As mentioned in previous posts the roll bar was lower than your head as seen on many Mogs with the Librands bar.
The factory Plus 4 Super Sport (pre-CX), fitted with the Safety Devices cage, had the same issue - my head was above the roll bar, and I believe most people would be similar if they were circa six foot tall.
As has been mentioned above, it would appear safe clearance does is not easy to achieve, for all heights of drivers, whilst having an operational soft top in place.
However, perhaps Safety Devices are also worth a call - they have been very helpful when I have spoken with them in the past.