Ah makes sense. So, drill small hole in the base of the heatsink, but leave a bigger gap in the fin area such that the screw of the spacer goes thru heatsink base plus pcb, but the weight is is carried by the heatsink. Going to be a little tricky. Or maybe not use the heatsink hole for the spacer, but rather get heatsink bigger than pcb and use the outside area for spacers... decisions...
Another advice : Any issues with using thermal adhesive rather than screws/bolts for mounting pcb on heatsink? <-- cause we are no longer mounting heatsink on pcb, but other way round.
I wouldn't use only adhesive on a board the size of the K16 but perhaps it would work on the K1.
My personal plan was to use bigger heat sinks as a long bar with several K16s fastened using spring clamped bolts to the heat sink. This should put a little less stress on the PCB where it mounts but keep even pressure on the thermal pads. This may not be the best way as I've yet to experiment with different arrangements and for a commercial product it may be more costly and so less desirable if it only works as well as smaller heat sinks. But this way the mount holes only support the weight of the board and not the heat sink.