I have my flaked rice set to 37 (1.037). I find that rice, especially, has big potential. Certainly to the levels of a base malt. If, after you brew, you find higher gravity than anticipated for your system/process then you can bump it up to 40 for the next go-round.
Recently, using precooked basmati white rice, I found that I WAY overshot my expected gravity. Unfortunately, I was also using a new base malt malt, and also a new step mashing schedule on this beer. Since there were several variables to look at I haven’t yet concluded that the rice was the “culprit” but I strongly suspect it should be put in the 40+ ppg range.