PiezoFlush and QTR-8channnel-purge.tif file behavior

I have been reviving my backup 3880 that was placed into storage with PiezoFlush filled carts. All channels (including both PK and MK) are printing perfectly but I am still tracking down one particularly problematic “clog” on the LC channel. I have been printing the single LC purge file (many times) to see if this would correct the problem.

While I believe this has been asked and answered many times I will also ask it again for clarity: the three missing horizontal bars in the LC channel (as printed in a nozzle check) are ALWAYS in the same position. Does this indicate a “clog” or a bad head or perhaps some combination of factors?

I also printed the QTR-8channel-Purge.tif file and have a question. Here is a photo of that print. As you can see not all the printed “stripes” are identical. Should they be? (While it may not be obvious from this photo LLK, LK, and LC appear to be almost identical; M is darkest but only slightly so; LM and Y are very close together; and C and PK are outliers .) I measured the RGB values of these stripes in PS and compared them to the 100% patch from the QuadToneRIP Ink Pattern Page: they are the same. I think these RGB values were selected in order to print a single channel at a time. But do they also control the amount of ink that gets printed? This would explain why the “stripes” in the print in the picture are different.