Testing Information Architecture with limited participants

I understand that a way to test IA is through tree testing.

However, a lot of articles mentioned that tree testing requires at least 30 participants (best 50 participants).

How else can we test our IA if we do not have that amount of participants - let's say we only have around 5-8 of them.

Are we able to do "qualitative tree testing"? - not sure if this is even a proper term.

Meaning that while participants are performing tree testing, we will observe their behaviour and ask questions on why they chose to navigate a certain way to understand their mental model (similar to a usability testing but using sitemap instead of wireframes). If not, how else can we go about doing it?

We would like to think that testing with skewed data results is better than testing with no results.