Why does Bandwidth setting affect call quality?

[teamits]

I'm kind of half asking and half documenting this... I recently set up an SG-2100 at home and afterwards added the wife's Teams traffic to the VoIP queue. She immediately complained about video call quality, despite having plenty of PC power on her brand new PC and plenty of bandwidth. The shaper had been set up using CBQ and the VoIP queue was 200 Kbps borrow since it was originally only for voice.

After some test calls to each other (via Teams) we found quality was drastically better either with that traffic not in the VoIP queue, or what I finally did was bump up the queue bandwidth to 3 Mbps to be above the usage for our test call.

So is that right that the queue size affected this? My understanding was it would just borrow bandwidth from the other queues as needed.

Other settings were based on the percentages from the wizard, e.g. for WAN (upload):
qInternet 10752 K (borrow unchecked on this one)
qACK 2048
qDefault 1024
qOthersHigh 1024
qOthersLow 512