One of the best guides to understand which waza work in which situation is Chiba sensei’s book and DVD set “Perfect Master” , where he devotes a whole section to which techniques should be used in which circumstances. If you can get your hands on a copy this explains a lot about kikai or opportunity, whereas most kendo books describe technique in isolation.
There are of course some very obvious examples of shikake and oji waza that have a probability of success in different circumstances. Men works for tall people against shorter opponents, dou and kote are more likely to help smaller kenshi against the tall. Tsuki too works for small people, which was regularly demonstrated by Arima sensei of Osaka Police.
As we discussed, kaeshi men is difficult against a taller opponent as their hands or shinai get in the way of the target whereas kaeshi dou or nuki dou are much more likely to succeed. Helton points out that at a height of 2 metres suriage men works for him. Strangely enough at my 1m 73 it also works for me, but I think that is because we are sliding up against a downward strike so both shorter and taller people can use it successfully. On the other hand kiri-otoshi is almost impossible against a much taller opponent.
Against jodan we have a whole new set of challenges regardless of the respective height of each player. I would guess however that many jodan players are relatively tall. In this case as well as the text-book tsuki, keeping your shinai in hirasegan and threatening kote and switching to men or threating men and switching to hit kote are worthwhile ploys. Kaeshi men too seems to work against jodan regardless of height as the jodan players men is open once he makes his attack.
Nito is a nightmare. Variations of techniques against jodan are still relevant, but the kodachi is always there to block men attacks. In this case tsuki and dou are the major targets.
In all of these situations practise and experimentation are the only way to find what works for you against different opponents, and if you train regularly with the same few people, it is worth visiting other dojo to broaden your selection of partners.