The short-term repeatability rating of the i1Pro2 (a $1500 dollar instrument) is .1 so a spectro that is 5 times cheaper is fine at .21.
Remember, you are measuring from L90ish to L24ish. So your standard deviation is only 1/314th + you are smoothing the measurement from there (partly due to this deviation but mostly for other reasons).
aka, don’t worry about it. Your brush-mark deviation is way more of a thing than the measurement device.
best,
Walker