see this often times on GT40´s . makes no sense at all for me because there is still enough room to slip ( dimension from inbetween your legs to the front end of seat). Lap belt is more pulled forward than downwards, this will loosen the lap belt in case of crash.
Theres is only one way to do it correctly, thats the way the lap manufacturers detail very much in there installation documents. ( check out the SCHROTH site). Every diviation from that its dangerous.
Of course this means extensive modification of seats and well thought out belt mounting/routing points in most of the replicas ( also on originals, because the where far away from the optimum as well).
TOM