"Suf-" is actually a variant of the prefix "sub-" meaning "under," "below," "beneath," or "lesser."
Here are some examples:
* Suffuse: To spread or fill (something) with a color, light, or feeling (meaning "spread under" or "spread below").
* Suffocate: To kill or die by cutting off the supply of air (meaning "to stop the breath from below").
* Suffice: To be enough or adequate (meaning "to be enough under the circumstances").
While the prefix "suf-" is related to the concept of "below" or "under," it does not consistently imply "always."