After declaring a new back box, my insurers (AXA) want to know the power increase - and Im not sure what to tell them!!

I've put a Scorpion SS BB on a MY00 classic, mainly to improve the sound of the car. Now I'd always thought that BBs didn't really affect power output without the centre section and downpipe also being changed. Is this correct?

An ideas on what should I be saying to the insurance company?

 

I'd tell them that it's designed as cosmetic, and will definitely be under 5%

 

I'm insured with AXA, I pay £1300 for a 2001 WRX. I called htem today as I was just about to book a full scoobysport exhaust and the b******s told me it would be an extra £400