I am Following the 2023 "Functional connectivity MRI quality control procedures in CONN" manuscript while performing some quality checks on my denoising proedure for two task-based datasets. I will noticed that my distributions of FC values are quite tall and narrow. I read this section of the paper I mentioned above that might explain why but I am not sure.

"No individual runs were identified as potential outliers after
denoising from visual inspection of these results. Site #6 included
several runs with distinctive narrower FC distributions, but these were
associated with scanning length that were considerably longer
(identified in the Figure 9 DOF distribution as having significantl
higher degrees of freedom compared to other runs in this dataset)."

My two task-based datasets have 700 and 750 volumes both with a TR of 0.8 seconds.  Because of my TR value I am not low-pass filtering and noticed that the FC distribution became much more tall and narrow after setting the low-pass filter bound to 'Inf'. I am only using WM and CSF CompCor components, 12 realignment parameters, and scrubbing to denoise my data and the overall mean of the FC distributions is very close to 0 for both of my datasets (i.e., mean=0.005+-0.002 sd=0.053+=0.009 and mean=0.005+-0.002 sd=0.056+=0.008).

Any advice on if my tall, narrow FC distributions should cause me concern would be greatly appreciated!