create /tmp with ffs vs. tmpfs ?

[Steve Rikli <sr%genyosha.net@localhost>]

I'm re-installing several old and new systems with NetBSD 10.0, one of
them is a 32-bit ITX PC, with VIA C7 CPU.

It has small memory (1GB max) but plenty of disk (128GB SSD). sysinst
says default size of "25%" for /tmp; from experimenting with other PC's,
I believe that's "25% of main memory" (RAM) with tmpfs.

Two questions:

1) is my understanding correct? I.e. does tmpfs use main memory for
   backing, rather than swap or something else?

This page says memory first, then swap:
https://www.netbsd.org/docs/guide/en/chap-tuning.html#tuning-system-mfs
so I'm mostly just checking.

2) can I configure /tmp as ffs rather than tmpfs?

For reference, when this little system is running FreeBSD I typically
don't use tmpfs, and configure a larger amount of swap (e.g. 4GB), so
native buildworld activites can run.

I'm not sure if I'll do native NetBSD src builds on it, but I'd like to
leave room for the possibility. 

Seems like I should be able to (manually?) configure /tmp as ffs during
initial sysinst, or leave some unallocated disk space to do it later.

My main thoughts were to avoid using RAM for tmpfs and simply configure
a larger swap partition, or add a swap file, etc.

Is this reasonable? Am I overthinking it?

Thanks,
sr.