I would not get too caught up in the whole 'I got this score here' and 'this test went ok, but this one was a bit average' etc. I've been on both sides of the fence (some time on either side in fact - took me 5 attempts over 5 years to get in) and I can say (IMHO) that there is a 'big picture' behind selection that most candidates are blind to. When I had a chap or chapess to assess, my biggest concern (medical asside) was 'would I want to go to war with said person' (or 'would I want said person to support me', 'would I trust them', 'do they have the potential' etc).
Selection, IMHE, is a game. I failed four times (well, actually five - but that's a long story...ok so a bunch of you know who I am now...!!!) because of various bits and bobs. My second fail was for the same reason as you - I came over a bit 'meek' in the interview. So, I did some research and worked out what it was they were looking for in a candidate - this got me further through the process but I ended up getting rejected all the same (well, initially). Seeing it from the other side of the fence was an eye opener and a half!
I'd love to say 'just be yourself', but I have to say 'project what they are looking for'. It's a game, learn the rules, play hard. Be persistent - it's worth it, it really is.
MT
ps) Please take/dilute this with the appropriate amount of salt because I went through the whole process 'One hundred billion years ago - woo hoo haa hhaa haaaaaa' (little finger in corner of mouth).