Hi, You hare doing DTA with some speed chosen by you or given by the equipment. Then at any specific temperature the specimen is not in thermal equilibrium. So you get an undercolling or an overheating
So two comments
if the speed is chosen more slowly then the values should show reduction of the difference.
many processes are non stationary. If you choose the same speed at DTA as in reality.Then you detect all the transient processesas with DTA as happening in reality.