Overstruck folles of Heraclius and Heraclius Constantine showing two mint marks

[Christopher H2]

Greetings,

I have recently picked up an interest in these coins from buying one and noticing its double mint mark. Joe was so kind to confirm for me that it was probably first minted in Cyzicus then overstruck in Constantinople.

The features of these coins are:
Two different mint marks (or two sets of the same?)
Often two sets of  on either side of the large 
Regnal year is often difficult to read due to the double-ANNO
The large M might have the remains of an upside-down M superimposed on it.

I will post my two specimens and I would love to see more, if anybody owns one of these please share!

FIRST COIN:
Heraclius and Heraclius Constantine
Struck in Cyzicus
Overstruck in Constantinople

[Christopher H2]

After receiving the first coin and instantly falling even more in love with it, I knew I had search for more.
I spent some hours browsing auctions and eventually found one with a very different fabric, color and obverse style. And this one was even originally struck in a different city. I knew I had to get it! I placed a generous bid and won. I am currently waiting to receive this one. Thankfully, seller's pictures are great. You can see the double-ANNO, the NIKO (part of the K is weak), the CON (the C is a bid weird-looking) and even a nice gamma officina letter.

SECOND COIN:
Heraclius and Heraclius Constantine
Struck in Nicomedia
Overstruck in Constantinople
Third officina

[Christopher H2]

Now if course my quest is to find out: what is the host coin for these overstrikes?

My best guess are folles of Phocas, for the following reasons:
He struck folles with an obverse of two people each holding a cross on a globe or a staff.
The O of his ANNO is often small and located close to the mint mark, see this coin:

(image courtesy of wildwinds)

Compare this ^oKYZ to that on my first coin, I see a strong similarity.

HOWEVER: This only works for the Cyzicus folles, as the folles of Phocas struck with NIKO mint marks do NOT have the large M but XXXX to denote 40 nummi, and also do NOT have "ANNO" to the left of the denomination, but above it!

So I will have to do more research once I receive the second coin to determine the undertype!

Thanks for reading and I hope somebody will have coins or insights to share!