hey there 60cal,
my T5 lights dont sit exactly on the dome, but are elevated about one inch from the top due to the patent design that they have that holds the light just above the plastic so it doesnt heat the plastic and melt it or burn plant tops that press against the top of the dome. some of those pics are a week old some of them are just a few days old, i will take a new picture of my shop seeds in their dome they have almost reached the top of the dome and are looking great!
my MH is just temporary right now while i get my T5 set up. the MH is a 400w that is just supplying enough light for them to not die or go into flower on me. once i get my room setup i will have my mothers (hopefully) all under T5 lights while under the 400w i will have 1-4 plants depending on the size or style of grow i am wanting to do in the following flower.
now i have a 1000w and 600w ballast and multiple hoods to where i could setup just a 600w and 400w in veg and run all under them but for two reasons i decide not to..
1. cost (as goes for most everyone) i dont see a point in running a combination of 1000w (600+400) for my veg room when i could get away running some T5
2. i dont care to have my plants grow super fast, under T5 they will grow healthy and slow compared to healthy and fast..
3. less heat to have to worry about
I&i
Edit : rambled forgot to answer, yes i put the light on my dome before the seeds sprout and i dont pre germinate my seeds. i believe i posted a post a couple pages back showing me doing my seeds. then just put the light on the dome and let the humidity build up and stay in there.