House move - one car insurance cheaper, other gone up?

We've moved to a new town. We have two cars insured with Admiral, both on single car policies. We changed the address, just as a mid-term amendment. All other policy details stayed the same - both still kept on a driveway overnight, annual mileage unchanged, etc.

After admin fee, hubby got a small refund as his premium went down by about £40. Mine went up! Only by a fiver (plus £20 admin fee of course!) so I'm not really upset about this, but I'm wondering why and if that sounds right to people?

The only difference is the make/model of car. Obviously insurers rate postcodes differently, but within a given postcode do they rate specific cars differently?

As I said, it's a tiny amount, but if that sounds wrong I'll query it again...

We'll shop around at renewal of course.