My females all curl up directly over the heat when they're gravid. I assume they know what they're doing. I keep the same temperatures year round--75 to 80F cool spot (that depends on room ambient temperture), and 90F hot spot. I do not allow my gravid females a basking spot over 90F, because they often lay eggs directly on the heat tape, and I want the eggs to be safe.
I have gotten very few slugs this year. I did have one female lay an entire infertile clutch, though, and another with several infertiles, but all of my bred females laid eggs this year, and the majority are all good.