The installimage sizes were bumped in 2022 because of some growth, and
the case for not-xz sets went to 4000 (MiB). That's just over what a
lot of "4 GB" flash drives are, but seems obviously intended to fit.
The actual usage of the filesystem, from a current build from earlier
this year (with non-xz sets) is:
/dev/dk1 3.7G 833M 2.7G 23% /mnt
and similar for netbsd-10 built yesterday, so we can afford to shrink
slightly. Drop to 3800, which is still huge, but will make 4 GB flash
drives work.
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