Why prefer a Type 73A?
F6 runs with two kinds of trains, and where you sit with a dog differs a lot between them.
Type 73A (electric train). The dog seats are a compartment of their own at the end of car 3: seats 155–174 behind a partition, set aside for people travelling with animals.
Type 5 coaches (locomotive-hauled). The dog seats are the back half of car 2: seats 29–68, in the same open saloon as everyone in seats 1–28, with no partition between.
With the switch on, Type 73A trains come first under Best match. Other trains are still listed below them.