The hitboxes are the same as they are in other servers, the tick rate is also the same.
It could be since the server has a stronger connection, some of the rates are allowed to be faster, leading to a different feeling of things.
Personally in all the times I have played in the server I have not noticed a change, I still shoot people in the head just as well as I did before.
There really isn't anything I can do for you in that department.
I think the most likely thing that is happening is the change in location is changing the lag compensation for you. While it is still acceptable, you have played on the previous server enough that you are used to the old server, and your play style has molded around that, this causes you to notice the difference and it throws off your shooting.
I on the other hand have always been used to large variations in lag, so I don't notice a difference. You will just need to adjust your play style.
Unless you have a specific idea on how to "fix" the hit-boxes, if you do let me know, otherwise... tough
For the karma, it seems to me to be at an acceptable level, the average karma in the servers is ~850-900 which to me is an acceptable level, perhaps a little high if anything.
So I have the correct average karma on the servers, I suppose the best thing I could do would be to change it so it feels more "fair" to the players, even though it seems to be for the most part.