hardcoding to 19 should work, also you could just change PRIO_MIN to PRIO_MAX which would basically do the same thing, (technically PRIO_MAX is defined as 20 in the linux kernel source)
I agree that there authors saw some practicality in changing the priority depending on what the function is doing, but personally Id rather just have it not touch the priority at all, as the program will work just fine sitting at lowest priority all day.. I dont want it ever stealing any priority from any process regardless of what the thread is doing.. (maybe it would be a good suggestion to make this a command line parameter to disable/enable automatic priority adjustment - Im sure theres many who would prefer to keep the automatic priority scheduling in place, but also plenty that don’t want any part of it)