Chromatic kalimba: possible tuning layouts

A customer recently asked me about potential note layouts on chromatic kalimbas.

I have crafted instruments with chromatic notes immediately adjacent, in linear ascending fashion, as well as Hugh Tracey style, where the chromatic notes are on the back surface of the instrument. I have also found a nice way to combine approaches, and essentially take the Hugh Tracey diatonic layout, and add chromatic notes adjacent to each pitch. This gives more pitch separation than the linear layout, but less than the Hugh Tracey arrangement.

I am not a physicist, so I have to go on observation of the work I have done.

I have found instruments with chromatic notes closer to each other to have more pitch separation. C and C# have very few overtones in common, so notes struck tend not to excite their neighbor notes by harmonic resonance. If there is a loss in sustain (from the fact that the note is not supported by sympathetic resonance of nearby notes) it is so minimal as to be not noticeable. And, a well-constructed kalimba could be built using dense woods to enhance sustain and clarity.

Hugh Tracey-style puts triad notes (chords) next to each other, giving a harmonic resonance- a very rich sound where the notes tend to blend into a wash of whatever the scale its tuned to. The harmonic similarity is only skin-deep though; if the instrument is tuned to equal temperament, even the I to V relationships are very slightly out of tune, and have little overtones in common. There will still be more overtones of a similar, if not exactly equal, resonant frequency.

Therefore, my idea is that if you want more of a modal, harmonically rich sound (sounds great, but only in the given mode or key) then go Hugh Tracey style and separate the notes as much as possible by grouping into triads. If you are musically more adventurous (most people using chromatics are!) then use whichever key arrangement gives you better access to the notes- the pitch separation will be there and I don't hear a major loss of resonance or damping by neighbor keys,

It is interesting to note that Zimbabwean mbiras are tuned with ascending scale tones immediately adjacent. The right hand notes are half and whole steps apart. There does not seem to be a problem in terms of richness of sound and resonance there!