Questions on pg_dump

We are doing some additional testing of our backup strategy with the goal of
moving from the text dump to the custom format and have some questions about
pg_dump -Fc.

Question 1. Why would the custom format be larger? pg_dump -Fc -Z 0 this
morning was 88GB while the normal pg_dump last night was 82GB. We have not
had that much growth in the few intervening hours. We were expecting the
-Fc to be at the most the same size of the text dump, and really expecting
the -Fc to be smaller. Any explanations? (We are doing timing with various
levels of compression and with the use of external compression to see what
gives us the best compression/time, so that is why the -Z 0 test.)

Question 2. With the -Fc, how can we verify a successful backup? With the
normal pg_dump, we are examining the end of the file looking for:
--
-- PostgreSQL database dump complete
--

Is there any sort of token like that with the -Fc that can be used to verify
a successful backup?

Thanks,

Chris