I then throw the geometric vs. the optical center into the ring ... the latter is recommended for attaching handles - but of course you should attach your handles wherever you like best. If you can't decide: Get two sets of cheapest fronts (or have particleboard cut at the hardware store) and try it out ...
I myself have mounted my handles - as an IKEA expert - in the geometric center of the narrowest front and attached all other handles at the same distance from the top edge.
Just flipped through the catalog... interesting how the handles on page 10 are NOT centered, but on page 13 (same kitchen, same spot?) they are, because it somehow looks better.
On p. 10 it would not be possible to attach the handles in the middle and align them on the adjacent tall fronts with those of the narrow fronts. The handle would then sit on the slopes of the panel or just above on the tall fronts.
Yes, I see that. Nevertheless, two pages later the apparently same spot (close-up of the buffet cabinet of the same kitchen) has the handles in the middle.
That is definitely a different kitchen, it now has a blue cloth with it. Many pictures have meanwhile been virtually assembled on the computer. Or the handles were moved on the computer for the close-up shots because it looks better.