So, what's the proper way to increase the flow on these pens?
The proper way? Change the ink, I suppose; I have about a dozen Pilot Capless pens in my household, and I've yet to encounter one that didn't write well or properly out of the box as a writing instrument. You could change the ink by switching to a different one with more 'flowy' characteristics, or you can alter the ink you want to use, at your own risk, by adding chemicals of some sort to it (but that, as far as I'm concerned, means you're no longer using the ink as sold by its manufacturer and as designed/defined).
Or you can acquire and install a Medium nib into your Pilot Capless pen, if you're using a Fine one at the moment. In my experience, the M nib are significant broader and wetter than the F nib, so much so that I dread the M nib and it stayed in my drawer unused for years. Just to be clear, I'm talking about increasing ink flow as your question was literally about, and neither about giving you as the user more control or doing it at the lowest possible cost or risk.
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