It seems like there's a pretty heavy emphasis on "Success Rate" thus far in the discussion (i.e., how to maximize the number of ingredients you can put in to maximize your success rate), and I think that's probably a bit misguided.
The Success Rate it's giving you is the percentage chance that you will receive any buff -- but it's important to note that not all buffs are created equal, and in fact some buffs may be inconsequential/worthless to many players. For instance, right now my city has a massive oversupply of mana, seeds, AND unurium (tail end of Ch19). I am basically soft capped on them when factoring in decay; buffing these productions for me is worthless. Similarly, while I wouldn't call the Goods production buffs *worthless*, they are pretty much inconsequential for me right now; I'm certainly not going to use time boosts to maximize their value, because I have other much more valuable things to spend time boosts on. The Goods production buffs basically amount to a free MM spell for me, and I have plenty of MM spells sitting around that I'm not using right now.
The most valuable things for me are the military buffs, and they're arguably the only buffs with any value for me at all.
So, if I maximize my "Success Rate" by adding in as many ingredients as possible, what I'm really doing is diluting the percentage chance that I receive buffs I actually care about.
Another way to think of this: for simplicity's sake, let's say there are only 3 buffs available to me (Buff A, Buff B, Buff C). Let's further say that I do not care about Buff A or B at all; they are inconsequential to my city and will not materially help me. Which option should I choose?
Option 1:
Buff A = 33%
Buff B = 33%
Buff C = 33%
Overall Success Rate: 99%
Option 2:
Buff A = 10%
Buff B = 15%
Buff C = 55%
Overall Success Rate: 80%
The smart play for me here is to choose Option 2; while my overall success rate is lower, my actual success rate (i.e., success rate on buffs I actually care about) is higher.
That's how I played it this week; I placed 5 Mana Shell, 5 Flying Iris, 5 Nightshade Blossom, and 4 Mocking Tongues. I was only able to put in 19 ingredients (whereas if I had spread things out, I could have placed 23), so my "Success Rate" was lower than it could have been -- but my percentage chance for military buffs was MUCH higher.
I ended up receiving the Barracks Strength buff, Training Grounds Strength buff, and Merc Camp health buff (and a Mana buff that obviously I don't care about). I'm pretty happy with this week.