To me, if the technique is not over with very quickly (with blending) what many people (unaquainted with martial arts) naturally try to do is to pull their limbs into their body to protect themselves. i.e. you can blend with someone when there is stong direct movement, but if they (uke) ever realise you're trying to do something they try to resist everything and keep pretty still (or pull backwards). Therefore, although we often practise some 'blending' on uke's part for training, this is just training until we can move with uke e.g.
if we do ikkyo, but they resist as they realise they are going down (and we weren't fast enough or didn't blend well), as they start to rise we allow them back up & do another technique (e.g. irimi-nage or kote-gaeshi etc). However we can't learn everything at once so its pointless saying 'try to go against everything I do', else it does become dangerous.
When I refer to resistance it is a static technique where uke just focuses on pinning you arm/hand in one place and tries to hold it there (unrealistic, but an important aspect to deal with) - I don't mean just being awkward.
I can really sympathise with Richard, I've had the same problem myself and the only solution I can think of is to actually attack uke and then use his response.