Howard, I use a presoak at the same temperature as my developer. This brings the tank to the correct temperature and helps to ensure even development. I soak the film for 1-2 minutes--no more.(posted 8256 days ago)The other important step is I keep the film during the entire developing stage in a water bath, which is set to the developer temperature. I use a large enough container to ensure that it will not fluctuate during the development cycle.
If you follow these steps, you should achieve consistency.