but most insurance companies will only go to 9+ which is a horrific con as usual.
Not if they apply the maximum percentage at nine years, crediting you as if you'd had 10 or more years accumulated periods of no claims.
Anyway it's a percentage discount, applied to a base premium. The base premium varies. For example:
Insurer 1. Base premium £200 - Percentage discount 20% = Premium charged £160
Insurer 2. Base premium £1000 - Percentage discount 20% = Premium charged £1,800
The risk (the individual insured) was, for the sake of this example only, identical. The percentage discounts are identical. The sums though differ. Logically, you'd go with insurer 1.... but you never can tell with bikermates, some would see the £200 discount as offered by insurer 2 as the better deal, after all the piss taking insurer 1 was only offering £40; the rip-off cnut.
Here's a tip. Forget all about the discounts, how they are worked out and / or if the chimp in the call centre got them right. Just listen to the final net premium the chimp offers you. It really doesn't matter if he used your postcode, your inside leg measurement, your mum's middle name or the circumference of Pluto to arrive at the figure. If you are happy, buy it. If not, call him a rip-off git, burn his house down, kill his children and go somewhere else.
PS Do though listen to all the other blurb the chimp chirps on about, like fees for amending the policy, fees to terminate the policy, security and garaging arrangements, auto-renewal and all the other 'hidden' rip-offs the chimp factory team dream up to hit bikermates in the cods with.