There are some technicalities involved, but the fact of your being physically present in the US for more than 183 days in a UK tax year is going to seriously complicate the question of your "residence" for tax purposes (on both sides of the Pond). That's why they limit the B2 visa to 6 months' duration - and then expect you to go home for a significant period of time.

I'll leave to Fatbrit and Twostep the question of whether your plan to renew your B2 visa based on a fortnight back in the UK is even feasible.

In any event, I'd say you're skating on very thin ice.
Cheers,
Bev