I sell fleet insurance mainly (but a lot of other non-motor classes too) and fleet rating is different - we look at burning costs per vehicle primarily, which is crudely just the average claims cost per vehicle over the last 3 or 5 years. Typically the sorts of factors largely ignored in fleet rating are: -
Postcode
Mileage
Drivers with convictions <6 penalty points
Drivers ages
Drivers experience
Vehicle modifications/additions of tools of the trade etc
Garaging details
Whether the vehicles are owned/leased/rented/borrowed
It's pretty crude on the face of it but there's an art in getting an enquiry from a client running a 100 vehicle fleet - helping them to see where the claims costs are coming from and fixing the problem. Often what we have to do with fleets is dangle the carrot so we offer a price for them to carry on doing jack **** in the way of risk management and then a more attractive option assuming they solve their accident problems - the saving often pays for the risk management needed. Fleet operators generally can earn a kick back profit share payment if they claim less than 10/20/30/40% of their total premium spend - that tends to sharpen the mind when they see the possibility of earning £30,000 profit share for a clean year.
Still hard work though because they're generally reluctant to admit they have a problem - fleet operators blame everyone but themselves for high claims costs. It's a real head up own backside scenario day in day out.