The 2nd set of measurements look a little closer to what I hear on my 4C, i.e. larger 1k bump that brings mids/vocals close. The larger 6.5k peak is expected with the TWFK (WBFK half) tweeter whenever measured with silicone tips, though I think the peak feels relatively controlled in the custom 4C (corroborating the findings of Kunlun the cat). I've yet to come up with a plausible explanation of what certain resonance peaks sound less prominent when the acoustic output interface encompasses a large and solid surface (as with CIEMs), as I find the phenomenon has less to do with insertion depth and residual canal volume than it does with compression of quarter wavelength resonances when reflecting away from an irregular surface (soft silicone tip).