pic: Flipped Transmission By SteamPunk #1577

Steampunk 1577 has recently been working on a flipped transmission for 2 cim motors in 1:4.66 ratio.
The transmission is made of 3* 5mm (~0.2") aluminum plates, 2* 44t 20dp gears, 2* 12t 20dp gear (for cim) and a 56t 20dp gear.
It’s designed in two levels - the first level decreases the speed (1:4.66) and the second level passes the rotation to the wheels’ axis.

While designing this we used this formula in order to calculate the center distances:
C = (N1/DP + N2/DP)/2
Nx = number of teeth on gear x
DP = diametral pitch

We wondered whether should be any extras added to the result of the above formula?

Would like to get your opinion,
Amit Shavit, SteamPunk #1577, Israel.