Hi David:
Try the "side entrance," meaning near either the left or right connection point of the edge of the soft palate with the extreme back of the roof of the mouth. Depending on personal anatomy, one will be easier to reach than the other, and whichever one it is will always be the shortest route into kechari for you. If you go in with the tip of the tongue there, the tongue will then slide to the center behind the soft palate and uvula. That way you are going around the uvula, so to speak, and it will be less likely to fold up under the tongue, not that there is anything wrong with that. Once stage 2 is in full swing, the uvula will slide back down under the tongue even when it is folded up on initial entry.
Also, once stage 2 and beyond are well established, the practitioner can go in anywhere across the back edge of the soft palate, including "up the middle" through the uvula. The point of entry matters most in the beginning, when minimizing the distance and getting around the uvula can make the difference between getting in and not getting in. This is when finger help (pushing the tongue back from underneath) comes in handy too. Later on, these fine points don't matter much anymore. It is just in we go, wherever and whenever we like. No finger help is needed then either.
Victor's suggestion of "going forward" over the top of the back side of the soft palate is a good one. When we are in stage 2 especially, the feeling is much like the tongue is laying flat on the bottom of the mouth, except it is laying flat on the "second floor" instead, which is the top (back side) of the soft palate. Stages 3 and 4 extend forward and up from there. It is a lot like sticking your tongue out, except the tongue is going forward and up instead of out the front of the mouth.
That way you can stick your tongue out at someone without them seeing it, and be stroking the "secret spot" for ecstatic conductivity and enlightenment at the same time!
The guru is in you.