Aha! That’s not the right way. Same discussion here Review: Manker MK34, 12 XP-G3, 3x18650 Floodlight starting from post #161
Although it is possible that you have derived the right conclusion that the 219B is putting out more lumens than 219C (meaning something is wrong with your light), it is tricky to use the method you described. Try a ceiling bounce test, and see what differences you get in lux values; this should be much more accurate.
Edit:
Basically, the 219B and 219C may have different domes, resulting in different optical properties so the same light output of the two types of leds will result in different lux values. This means you cannot use lux values obtained by shining the light at the meter directly to derive lumen values.