Best way to bucket fill ink drawing?

[southofmotown]

I scan a black ink drawing on white paper. If I'm using a bucket fill, what are the best settings so that the black lines are preserved and dominant? Normally I don't have any problem - I just make sure the lines as thick and dark before I scan. However, on my most recent drawing, the bucket fill swallowed up the lines more than normal - I can only guess that my settings were somehow changed (unbeknownst to me) from what I am used to. I usually just set the bucket threshold to 90 and it does a pretty good job. Thanks for any suggestions!