Right on the front, wrong on the back, or a story of 3 heels (mine included), or a Monty Python skit: 'now for something completely different'. Z owners know this: others zoom in fully on the top of the z heel and you can see that the last cm or so from the 24th fret towards the body is a ramp that does not contact the body, perhaps for some percussive snap and/or more coverage of the neck on top. The longer extension of the bass-side cutaway and deeper bolt pattern on the back may compensate. On the AB-I, we have a Full Frontal Heel shot: no slouch on slap though: I suspect the design of the back on the AB-I may be part of the 'compact' concept. However, switching between them, the first-fret reach doesn't feel hugely different--they are both compact, in slightly different ways. If the AB-I hangs with first fret slightly closer (i.e., if so its << 1/2") then it also tends to shift my plucking hand toward the neck vs more of a bridge plucking position on the z (again, slight if true). When the squinting is done, these basses hang very similarly compared to other brands/models at 35" 'B' multi-scale or longer.