Configure V8 DefaultWorker threads in yaml

We are using the wasmervice bootstrap extension in yaml as below

bootstrap_extensions:

• name: envoy.bootstrap.wasm typed_config: "@type": type.googleapis.com/envoy.extensions.wasm.v3.WasmService singleton: true

When we have this in the yaml even after marking "singleton : true" we see 16 "V8 DefaultWorker" threads started on a 32 cpu box. Is there a way to limit these in the yaml with some parameter ? Or do I have to change code and rebuild envoy ? --concurrency doesn't help in configuring these as that is only for worker threads. Tried doing a google search for this issue but nothing turns up.