I think the instance limits just make sure you do not scale in beyond the minimum of instances, if you delete the instance manually, it will not scale back to 2.
The autoscale just happens when it meets the autoscale condition, for example, you deleted the instance, then the (Average)Percentage CPU > 75, the instances will return to 2. If the (Average)Percentage CPU < 25, it will auto scale to 2 at most, the minimum
decided it. But if you delete the instance manually, it is not decided by minimum
.
For more details, see Define autoscale instance limits.