Upper seat belt anchorage height

[Matthew]

Can anyone tell me what the limits for the height of the crossbar on the roll bar are to conform to the required seatbelt mounting height?

I've found the directive referred to in the IVA manual here but at the moment it's not making a lot of sense to me.

The base of my seats are currently more or less on the floor, but I want to leave a bit of leeway as I'm not sure I'm going to be able to see over the scuttle

Thanks
Matt