The ones I've got had a choice of lenses and also allowed some adjustment
in the horizontal plane. So they're mounted in the 'conventional' place.
They seemed to cope ok with a cat when I last had one, but she was fairly
old and didn't jump that high. ;-)

Yes. I'm familiar with those types of PIR. Problem is that if they're
mounted in the conventional place and a pet alley lens or PCB position is
selected the overall sensitivity is quite poor in relation to a standard
setting/lens. You can't have it all ways. Pet proof always means less
coverage/sensitivity. The other common method is to use multiple pulse
count. Most PIR's have the capability to pulse count to 4 but to be honest
the average person moving at normal speed will only cause the average PIR to
actually trip once or maybe twice at a push so it would be possible to walk
through the room without activating the alarm.

So, it's either per alley dual-tec, perimeter protection or poor protection!

The other line of thought of course is does the kitchen actually need space
protection anyway. Kitchens are notoriously bad for alarms. Cookers, hobs,
hoods fridges and washing machines can all cause false alarms with space
protection whereas perimeter is OK with these. Smaller kitchens, like
bathrooms, suffer from condensation problems and that isn't good for any
sensor. OK, if there's a Hi-fi, TV, PC and a whole load of NEFF appliances
then the area may need protection but if it's just a bog standard kitchen
why bother?! Protect the "house", not "the kitchen"!