To get a fluffy,crispy and soft south indian ulundu vadai recipe the dhal should be ground lightly coarse and in wet grinder you will get good aeration for the batter rather than mixer.
After you grind test it by adding the batter in a bowl of water and it should float this shows the batter is fluffy.
If you are not adding rice is just fine,it comes out perfect.
If you are grinding it in mixer then you have to beat the batter for some time so that it becomes fluffier and will get same perfect result.
Should cook in medium flame till golden.