Excellent info. I had not even thought that ridge might be an obstacle before.
classic chasis
Damn, I didn't think about that at all, sounds like our "./enter" key might have to become the function key? Then the rest of the cluster is: nav keys, arrows, numpad numericals, numpad operators.
PS. "0" can have the decimal "." as a fn layer.
PPS. Essentially this: but properly aligned etc... Each user can decide for themselves which section goes on which layer to match their usage patterns.
Most people, probably, predominantly uses the nav layer; so can set the nav buttons + cursors to default and numpad to function/meta layer, in effect getting a TKL. If, like me, you prefer a TK design: set the numericals + cursors to default and get that layout.
As a bonus, it gives a function key for those who chose a traditional ANSI layout on the main cluster.