FYI, I spoke to FluidOne a few weeks ago and learned some things which may be relevant here.
I suggest they simply made an educated guess on the distance based on the BT Wholesale FTTC estimates for the property and assumed some rule of thumb additional distance.
No. The property banding came from him entering my phone number/postcode into an OpenReach or BTW system; it's not estimated by the service provider, and it's not related to FTTC.
He said that under the old (banded) model, the instant price quote was generally the price the customer ended up paying. He knew of only one case where Excess Construction Charges (ECC) had been levied, and that was on a Band G property - 1500m to 2000m radially from the nearest aggregation node.
Under the new model, there's no instant quote at all. You can get a free non-binding estimate, which is a "desk survey" made by someone looking at OR looking at a GIS map, and this is supposed to take 2 weeks. Only when you place an order will you get the actual cost - and if you decide to back out at that stage, you'll have to pay a £245+VAT survey charge.
He said he knew of several people in the longer distance brackets were getting their orders in before the 23rd Feb switchover to new pricing, as he was expecting the installation costs for long distances to increase substantially. The costs for short distances (old bands A-D) he expected to remain more or less unchanged in total.
Fluidone only sell their services to business customers, irrespective of min term on any package. However with Cerberus you may be able to take out services as a residential customer on service contracts of 24 months or less but you would need to speak to them for clarification.
FluidOne intend to keep the 36 month contract period for FTTPoD, even though the OR contract drops to 12 months. Cerberus' webpage says they are dropping to 12 months.
I also came across a third provider of FTTPoD: Amvia. Their pricing sounds like it's in the same ballpark or a bit lower than FluidOne, but I don't have like-for-like quotations to compare. It's possible they are just reselling F1.
Speaking personally: I'm 500m radially from my VDSL cabinet, about 800m copper length, which means I get about 35M down / 5M up on VDSL; I guessed I would be in band C or D. However, I am actually in band G. That makes it clear that the aggregation node is not the cabinet.
Given that the total cost over 3 years on the old model was so high, I decided to take a gamble and wait and see what the new pricing turns out to be. I live in a cul-de-sac and I have some evidence that there is fibre running along the road that runs past the end. That road continues into the countryside, but less than a mile further along, fibre pops up out of the ground and then runs along telephone poles. (It's definitely fibre. It says "Corning Optical Cable" on it, and the junction boxes have laser warning symbols on them

)
I don't know whether OR would be able to make use of the existing cable which goes near my house, or would have to pull an entirely fresh one for FTTPoD. But I thought it was worth finding out.