if they are showing the tap root then germination is not the problem as you have germinated them
you say, you cant see them emerge from the soil ??
this part does not make sense to me, because if you are germinating them first, you do not want the seeds under the soil
the tap root goes downside into the soil or growing medium like rockwool or whatever, the shell seed end points upward at the surface of the soil
you can put them straight under the light at this point. the seed end will raise up and split its shell while the tap root grows downwards
sounds to me like you are putting them under the soil too far under after they have allready germinated ?
i think it would be much better for you to germinate them like you have, then put the germinated seeds in little rockwool cubes, wait until they grow seed leaves and the first set of true leaves and a little root out the bottom of the rockwool cube, then plant the little cube in your soil
peace