An insulin moving faster in and out would seem to reduce the length of zero basal.
Look at extreme cases as examples for comparison.
If my insulin duration was 15 minutes, a 30 minute ZB would mean that I had no insulin remaining. Certainly 30 minutes would be totally sufficient.
If my insulin duration was 10 hours, a 30 minute ZB would be meaningless. I would still have plenty of insulin left. So it would need to run the ZB longer.
I think it is much closer to my actual than the one that comes with loop.
Insulin does NOT last 6 hours in my body. Not even close.