gsettings set org.mate.panel.toplevel:/org/mate/panel/toplevels/top/ size is 28 by default in Ubuntu MATE 22.04.

Stacked system monitors (feature request)
gsettings set org.mate.panel.toplevel:/org/mate/panel/toplevels/top/ size 55 a lot of extra space is added:

Proposed solution to save space:

See this issue on Launchpad: https://bugs.launchpad.net/indicator-multiload/+bug/2028990