Are you getting more usable detail with a thermal monocular than with a fast prime and high ISO? I trialed a FLIR One Pro around 11 p.m. on a neighborhood canvass and it flagged heat, but the detail was lacking — probably situational, so check your local laws and do your own research.
Thermal’s great for detection, not identification — “detail was lacking” is normal, so use it to spot movement and then hand off to a fast prime in monochrome with a low-power 850 nm IR illuminator and diffuser (if legal) for faces/plates. Think of thermal like a metal detector: finds the treasure, doesn’t grade the coins. What focal length and ISO were you running on the low‑light setup, @OP?