More on Resonator Tuning

I did the first round of resonator tuning "by ear". Using a bucket of water to stop off the end of the tube I changed the water level until I got what seemed like the best sound. After making all the resonators I discovered I could measure the tuning of the tubes with the strobe by placing a microphone at the opening and taping the end cap. Most were tuned 15 - 40 cents sharp, but my "best note" had a resonator tuned 80 cents sharp! One of the "worst note" resonators was tuned 15 cents flat, (shortening it made a noticeable difference). I can understand the general finding of 15 - 40 cents sharp, since the functioning length of the tube includes the distance between the bar and the tube opening, but 80 cents sharp, that seemed a bit extreme. One of the great things about the overall design of this marimba is it's modular nature. I can make a new resonator (or note), easily install it on the instrument, then change back and forth, the old and new. Radically sharp resonators (70 to 90 cents) give a slightly punchier sound. But one would think that they would hardly work at all. Why is resonator tuning so approximate? I'm still pondering this one.