Culture victory possibilities

I've been playing for some time and I tried both Dictatorship and Republic politics, I was wondering is there a way to make culture victory possible while playing these two politics, because the rainbow disappears when playing dictatorship especially. sometimes when you play in war conditions, you need a large army to defend oneself or allies, but it's not always possible to feed such a large army except when you play dictatorship or monarchy, if your towns are close enough, so is there a possibility to make the culture only affects domain, without affecting the rainbow?

just destroy some military buildings when rainbows required. should not be required until last few visitors.  Hero can acheive 1 rainbow easy enough with perks.

Bers, possible to tell us the formula for rainbows please?  Seems to me it is some ratio with Pop/Culture. Similar to loyalty formula.

... except when you play dictatorship or monarchy

Since dictatorship has the culture reduction, for your kind of play it would have to be monarchy if you want to do culture victory. Yes, not as many globals possible, but you can't have it all.

Although monarchy domains aren't actually that small. And you can put towns not quite as close together if you can live with medium corruption (e.g. 10-15% in monarchy as opposed to 30 or 40% in "normal" collect/despot), and/or if you are good with other options of feeding a large army which I would assume you are.

Highest rainbow, 300 or better.  Culture squared, divided by (population times 3.5).