If you are thinking release and trying to manufacture one over small fences, you are terminally overthinking.
Stop thinking of a release as a separate movement and let the horse fold you as it goes over…of course, with small fences, theres really no jump to do that so just hold your position from 3 strides out and keep your hand still while the horse takes care of the rest. Sounds easy but we all tend to want to do something even when its not only unneeded but interferes with the horse. Its hard to change thinking on that. Some trainers don’t teach it well either, or just don’t know.
Ask your trainer about the neck strap mentioned upthread or grabbing mane and holding that until after landing.
We see the release but it comes from a strong position in the tack, not from moving hands, arms or shoulders.