First - you need to be open to changing whatever plan you’re using to extend a peak in the moment. If you extend it too long (for some people four weeks will be too long) you will run a high chance of killing the rest of your season. Be prepared to listen to your body and bail out early on the extended peak.
As to what approach you use to extend your peak - I’d suggest you grab those taper weeks from prior to your A race and just copy and paste them leading into the two following B races. How much time you take off after the A race will vary a ton, but what you describe could be a viable approach. Basically I’d want to remove a lot of TSS by removing endurance efforts while training to maintain my high end with the spiky taper workouts.
What you’ve described is a great start but remember to pay attention to your body during this extension of peak