your plant is trying to reduce its surface area to a:lose less water b: lessen the light intensity for itself.
You can up the humidity if you d like (personally i have never bothered) or dim the lights or hang them a bit higher. Both will make the plant lose less water.

I only do autoflowers outside during summer with natural light.
I dont care about the leafs crumbling a bit during growth because i can grow them a couple days more before to 12/12 and i like the idea that my plant gets used to low humidities before flowering (i see it as some kind of training) so they dont get a real shock when they bloom under the hps and the humidity drops dramasticly and i keep it that way to prevent bud rot.

For autoflowers It may be handy to give them the optimal values during growth because you have limited time.
A humidifier is not expensive and as long as you introduce enough airflow you wont get any fungus problems during the veg stage of the autoflowering procces.

Few weeks later, how do the plants look?