Tzitz- related: Mtznefes of Kohen Gadol

There is much discussion if Mitznefes of Kohen Gadol and Migba'as of Kohen hedyot were the same, similar or different.

See Tosfos Eruvin 95b, Tosfors Sukkah 5a, Rishonim on Yoma 12 and 25, and Tos Yeshanim Yoma 86.  (BTW this is the mekor to smething I posted on long ago, that there is place for 2 Tefillin on th ehead, if it's next to each other or one in front of each other; most of these sources hold in front of each other.)  (Ritva Yoma 25 cites Shimusha Rabbah there is no minimum shiur for tefillin but most hold it is 2 fingers).

Rashi, Ibn Ezra and Ramban all say Mibaas has more Pe'er.  My first reaction to that si that Tefillin are called Pe'er and that's why an avel doesn't wear them the first day (whether that is yom misa ukevirah only or also yom kevura is a different discussion).  Both kohen gadol and hedyot needed to wear tefillin (pe'er) with their head-covering, so perhaps because the Kohen Gadol had tzitz and tefillin in the tefilin area, but the kohen hedyot only had tefillin, part of the migbaas was on the tefillin-area (which was empty on the head) so the migbaas part on that area is called pe'er.

from Torahmusings
Ramman on Vayakhel-Pikudei 
Verses 27-29 tell us about the garments common to Aharon (and all later High Priests) and the ordinary priests. Verse 27 speaks of kutanot, tunics, for Aharon and his sons; Ramban thinks those were exactly the same.
The next verse mentions the mitznefet, Aharon’s head covering, and the migba’ot, the ordinary priests’ head covering. Ramban thinks they were made the same way, but worn differently—as he said in 28;31, a comment we did not see at the time. The High Priest would wrap the material around and around his head, to create a sort of hat, one that has an opening in the middle. Other priests would take that same material but wrap it in such a way that it fully covered the head.
Then, in our third verse of this section, Ramban points out that Chazal in Yoma 12a debated whether the avnet, the belt, of the High Priest differed significantly (he does not elaborate further, but Rashi to Yoma 12a tells us that the issue was whether a regular kohen wore a belt of linen or of mixed materials; the High Priest wore one of mixed materials throughout the year, and of linen on Yom Kippur).