Sometimes people experience kiln wash sticking to the bottom of their glass.
You need some understanding of what kiln wash is to know why the wash sticks. It is largely due to the chemical changes in the kaolin at fusing temperatures.
Opalescent glass does tend to pick up kiln wash more easily than transparent, and does it more at higher temperatures. It is the case that at higher temperatures and longer soaks, the kiln wash is more likely to stick to any of the glasses than at lower temperatures and with shorter soaks. This re-enforces the mantra of "low and slow" to avoid problems in kiln forming.
To achieve the same effects at lower temperatures as at higher temperatures, your rate of advance needs to be slower from the slump point to the top temperature. This additional heat work will achieve the desired effect with a lower temperature.
One kiln wash, Primo, does not contain china clay. If you use this and it is sticking to the bottom of the glass, you may be firing too high. Try a lower temperature with a longer soak to reduce the kiln wash pickup.