Why the prefetch size is not equal to the request size?

[shareisall]

In package rsocket-adapter-rxjs, why the prefetch size is not equal to the request size? In some case, I need exact size per request.

file: packages/rsocket-adapter-rxjs/src/RSocketPublisher2PrefetchingObservableToObserver2BufferingRSocketSubscriber.ts
line 86:
this.scheduler.schedule(() => this.subscriber.request(this.prefetch - 1));

file: packages/rsocket-adapter-rxjs/src/RSocketPublisherToPrefetchingObservable.ts
line 65:
this.limit = prefetch - (prefetch >> 2);
line 77~80:

if (this.received % this.limit === 0) {
  this.scheduler.schedule(() => this.subscriber.request(this.limit));
  return;
}