AVMutableComposition scaleTimeRange limits (iOS)

My experiments show that AVMutableComposition scaleTimeRange is limited to scaling up to 8x faster than the original composition.

This limit is not documented anywhere.

Is it a true limit? If so, is there any way around it?

Relevant code below, with some boilerplate abstracted into functions not included here:

   AVMutableComposition *comp = [[AVMutableComposition alloc] init];
  AVMutableCompositionTrack *videoComp =
    [comp addMutableTrackWithMediaType:AVMediaTypeVideo
    preferredTrackID:kCMPersistentTrackID_Invalid];

  AVAsset* asset = AddVideoToTrack(videoComp, kCMTimeZero,
                   CMTimeMake(startSeconds, 1),
                   CMTimeMake(endSeconds, 1),
                   videoFilepath);

  float initialDuration = endSeconds - startSeconds;
  CMTime startTime = kCMTimeZero;
  CMTime endTime = CMTimeMake(initialDuration, 1);
  CMTimeRange inputRange = CMTimeRangeFromTimeToTime(startTime, endTime);
  [videoComp scaleTimeRange:inputRange toDuration:CMTimeMakeWithSeconds(initialDuration / playbackSpeed, 1)];

  ExportWithSDAVAssetExportSession(videoComp);