In my experience and that of others, C16 mixed with 93 just seems to pull harder, it may be from different brands of race fuel. But I mixed Sunoco 112 one time and the car did not run as well as a equivalent mix of C16 (another brand), I wouldn't use C12 again.
If you have 8 gal of C16 and 8 gal of 93:
[8(116) + 8(93)]/16gal = 104.5 octane
Plenty for 1.8 bar, although I have heard some say the true octane benefit of C16 is higher than the simple math would suggest. The only drawback is lead with higher octane race fuel, but that goes with the territory.
As long as your total octane is around 103 or more , you should be fine at 1.8 bar.