I don't think the logic mentioned as proportions for mixie vs grinder are right for idli. 1 urad and 4 rice works in mixie as well for both idli and dosa just that the water used for grinding should be less and not like that for grinder. To grind urad, one can use water in equal measure as urad dal taken. Don't pour all the water in one shot. Pour little by little and grind in short durations / even pulse to get bubbles in urad. For for 1 cup unsoaked urad upto 1 cup water can be used in small amounts to grind. To grind rice, one can take 1/4th to a maximum of 1/2 measure of rice as water to grind. For 4 cups of unsoaked rice taken 1 cup to maximum of 2 cups of water can be used to grind. When I say cup - it is any measure that you choose to take. Tumbler, davara, actual cup measure, karandi / ladle, etc. For easy cold temperature fermention, you can use 1 spoon to a maximum few spoons of 1 time rinsed and then 10 minute soaked avul / flattened rice / poha ( uncooked ) OR home cooked white rice ( I am not sure if basmati rice will work ) for the day and grind it along with the soaking rice. Additionally you can keep the vessel ( non platsic ) containing the ground batter in warm water for sometime to ensure the batter is kept warm. Even a used cooker with warm water in it at the base cab be reused for this. For mixie grinding, Idli alone - 1 urad 2 rice is also enough Dosa alone - 1 urad 3 rice is also enough Idli and dosa common batter - 1 urad 4 rice is required Water as mentioned should not be a lot and grinding should not be continuous.
