Soaring: Does "Thermal radius estimate" (Soar.x1) have a lower limit?

After careful analysis of the data from a 45 minute flight, about 15 minutes of which was in thermal mode, I found that “Thermal radius estimate” (Soar.x1) is limited to values > 40 meters. Does “Thermal radius estimate” have a lower limit and if so, how can I influence it?

(I have set RTL_RADIUS to 40 meters and WP_RADIUS to 40 meters.)

Thank you for your answer
Stefan