Ok.It's been a few years since I worked there, but my best recollection is you'd have a tough time going beyond 17mm or maybe 17.5mm.
The biggest issue would be the string spread in the upper register and the outside strings falling off the edge of the fretboard.
The bass that all the hardware is from has a 80mm broad neck at the 24 fret and the gecko 6 is 84mm so I hoped it would do better on the gecko neck. And yes, on the current bass it’s a bit on the borderline in the upper register.