It's probably not only geographic distance, but also relative size of the subfield that plays a factor -
Ever since my PhD I worked with a relatively minor plant and have been doing so for the last 5 years, I now know all "major" people in my sub-field and they know me, which made finding unbiased reviewers for my thesis quite hard.
I regularly bump into all of them at the same conferences, they are the only ones who can gauge my work for committees etc. Citing them negatively would be career-suicide (well, it depends on the cited person - a few would probably be alright and be happy that their work is being improved, others would deny my existence. I've actually published one paper improving another guy's work and showing his flaws, I've included him as an author to soften the blow, which isn't unethical since he also supplied some data, he did some work).
If I would work in a bigger field (say, HIV) it wouldn't matter so much.
Ever since my PhD I worked with a relatively minor plant and have been doing so for the last 5 years, I now know all "major" people in my sub-field and they know me, which made finding unbiased reviewers for my thesis quite hard.
I regularly bump into all of them at the same conferences, they are the only ones who can gauge my work for committees etc. Citing them negatively would be career-suicide (well, it depends on the cited person - a few would probably be alright and be happy that their work is being improved, others would deny my existence. I've actually published one paper improving another guy's work and showing his flaws, I've included him as an author to soften the blow, which isn't unethical since he also supplied some data, he did some work).
If I would work in a bigger field (say, HIV) it wouldn't matter so much.