Hi,
your number seems to match the primary shards metrics of ~ 1100 docs/s pretty well. Quoting from the index stats API docs:
primariesare the values for only the primary shards.totalare the accumulated values for both primary and replica shards.
So I assume that the numbers you got are from the primaries but not from total.
With regards to the difference you also need to account for the different sampling rate (see xpack.monitoring.collection.interval in our docs) which is 10 seconds by default. These two adjustments should bring you pretty close*) to the numbers you see in the monitoring application.
Daniel
*) you can't get the exact same values as you'd need to sample at the exact same point in time as x-pack monitoring but that shouldn't be a problem in practice.