Doubt in pgbench TPS number

Today I got an interesting output from pgbench.
The scenario is executing SELECT pg_sleep(0.1).

$ cat test.sql
select pg_sleep(0.1);

$ pgbench -C -n -p 11002 -c 10 -T 30 -f test.sql test
transaction type: Custom query
scaling factor: 1
query mode: simple
number of clients: 10
number of threads: 1
duration: 30 s
number of transactions actually processed: 2883
latency average: 104.058 ms
tps = 95.799114 (including connections establishing)
tps = 124.487149 (excluding connections establishing)

Interesting thing is, the number from "excluding connections
establishing". 124.487149 tps means 0.008032 seconds per
transaction. Since the query executes pg_sleep(0.1), I think the
number should be equal to or greater than 0.1. Maybe a tolerance, but
20% of error seems to be too high for me.

Note that if "-C" does not present, the TPS number seems to be sane.

$ pgbench -n -p 11002 -c 10 -T 30 -f test.sql test
transaction type: Custom query
scaling factor: 1
query mode: simple
number of clients: 10
number of threads: 1
duration: 30 s
number of transactions actually processed: 2970
latency average: 101.010 ms
tps = 98.692514 (including connections establishing)
tps = 98.747053 (excluding connections establishing)
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Tatsuo Ishii
SRA OSS, Inc. Japan
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