i too worry about this, my ds, 3 today,takes ages to go to sleep at night no matter how tired he seems/how active he's been.
he used to do that lying there thing, and tbh i wonder if he has always done this, as not aware of it when he was tiny.
now he talks/reads(recites)his books or plays with his little cars for about an hour. used to go to bed at 6.30, moved to 7 recently, seems to reduce this period but still awake til 7.45ish no matter what!
he seems happy up there, is resting, it doesn't disturb dd, 13mo in same room. he too naps, 2hours plus most days, usually only takes 5-10 mins to settle. still stays awake on days where nap missed/interrupted so not sure that is reason.
he wakes up between 6 and 6.30-or is woken about then by dd. sleeps through, very active though will say he is tired sometimes-usually means he doesn't want to walk somewhere
i do sometimes worry he isn't getting enough of his sleep at night, but this routine does fit very well with us all and he is a very happy, calm little boy.
maybe like op dd, this is just how they settle themselves-like an adult always having a read or listen to radio in bed?
i do think ds may have always had a long though previously silent zone stage, as a tiny he took ages to fully drop off, even when feeding to sleep, and always used to see his eyes open for about an hour on car journeys begun at bed time etc.
as i say, my concern is that although in bed by 7, not actually sleeping til nearer 8, which i think late for 3. what makes you wonder dd sleep thing may not be okay? the silent thing can be quite unnerving though can't it!