CC2652RB: Limited by notification buffer on iOS

I'm running into some issues sending notifications to an iOS app—up to 5 of them every 250ms, each ~250 bytes. I appears that when all of these are active, the buffer on the iOS end fills to about 5 notifications. I've throttled them on the CC2652 peripheral side for now. If this is indeed my issue, my understanding is that something like voice over BLE wouldn't help, since it posts notifications, as well? The peripheral notifications are posted in a batch, and increasing MAX_PDU_NUM nor decreasing the connection interval has not helped. I just want to make sure I'm not missing something on the peripheral before I go down a debugging rabbit hole. Thanks again