Is the `size` parameter for tmpfs in fstab not working?

I am confused about whether my /tmp using tmpfs is respecting the size parameter that I gave to it in /etc/fstab:

My fstab entry is:

tmpfs /tmp tmpfs rw,nodev,noexec,nosuid,relatime,size=4G 0 0

But according to du, it is using half of my memory (which I understand is the default) instead of the size I meant to allocate to it.

 ~ df /tmpFilesystem     1K-blocks  Used Available Use% Mounted ontmpfs           65921428     0  65921428   0% /tmp

So is the size parameter simply not having any effect?I am working with Ubuntu 20.04

Edit I can mount it manually with

sudo mount -oremount,size=4G /tmp

When I do that /tmp is the expected 20.04 GB.

Edit: systemd status:

● tmp.mount - Temporary Directory (/tmp)     Loaded: loaded (/etc/systemd/system/tmp.mount; enabled; vendor preset: enabled)     Active: active (mounted) since Wed 2020-06-17 13:30:35 EDT; 8min ago      Where: /tmp       What: tmpfs       Docs: https://systemd.io/TEMPORARY_DIRECTORIES             man:file-hierarchy(7)             https://www.freedesktop.org/wiki/Software/systemd/APIFileSystems      Tasks: 0 (limit: 154317)     Memory: 76.0K     CGroup: /system.slice/tmp.mountJun 17 13:30:35 virtland systemd[1]: Mounting Temporary Directory (/tmp)...Jun 17 13:30:35 virtland systemd[1]: Mounted Temporary Directory (/tmp).

and journalctl -u tmp.mount

-- Reboot --Jun 17 13:27:50 virtland systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting an>Jun 17 13:27:50 virtland systemd[1]: Mounting Temporary Directory (/tmp)...Jun 17 13:27:50 virtland systemd[1]: Mounted Temporary Directory (/tmp).Jun 17 13:29:43 virtland systemd[1]: Unmounting Temporary Directory (/tmp)...Jun 17 13:29:43 virtland systemd[1]: tmp.mount: Succeeded.Jun 17 13:29:43 virtland systemd[1]: Unmounted Temporary Directory (/tmp).-- Reboot --Jun 17 13:30:35 virtland systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting an>Jun 17 13:30:35 virtland systemd[1]: Mounting Temporary Directory (/tmp)...Jun 17 13:30:35 virtland systemd[1]: Mounted Temporary Directory (/tmp).``