Going through an short range group agg. I have had barrels that shot their best very clean, and barrels that seemed to tighten as they got a little dirty. I never got more than three matches on a barrel before a patch cleaning that involved a lot of short stroking, reserving a second cleaning that included bronze brush work for lunch break. Some of this comes down to what powder and how much per charge. I was using 133, which did not seem to have hard carbon issues, given that I did a lot of bronze brushing.
On the other hand, when LT32 came out, I noticed that while not bad, it would require occasional use of IOSSO, not every time, but if one did not, it would eventually catch up with you. A friend, who exclusively used LT32 in his 6PPC found that using IOSSO about every 100 rounds seemed to prevent any accuracy loss due to hard carbon, and he got decent accuracy life on his barrels doing that. One thing that I do not want is to polish away the lapped finish, since that would cause jacket fouling issues.
Many years ago I read an interview of Tony Boyer which included his cleaning practices. Back then he shot T, and used a nylon brush full of IOSSO to clean the back 8 to 10 inches of his barrels, cleaning between every match. I believe that this was because T required it. This was before the advent of the hard nylon brushes.
Since that time, I have used the more ordinary black nylon brushes for IOSSO, but only infrequently. Friends that I have told about this method have used it without any issues on an as needed basis.
I think that using brush that does not put much radial pressure on the bore is the right approach.
Last year, when I had run out of IOSSO, I ordered Thorroclean and Thorroflush. I use the same kind of brush, wrapped with a square patch for the Thorroclean and find that it removes a lot of black for the number of strokes, but I still only use it on an as needed basis, which is more often for H4895 in my 6BRA because of the fouling of that powder. When I clean, I am not looking for a spotless mirror finish, which I believe that is a pit that new bore scope users can easily fall into.