Preview Screen-positions don't match

Why is it that a pose will look perfect in Poser and then you preview it in SL and it's totally off, i.e. hands and forearm will look as if they are resting perfectly on the top of your legs in a sit pose, and then in the preview screen they are floating above your legs?

There also seems to be a difference from the SL preview screen to what the pose looks like on your avatar.

As you can tell, I have no clue what I"m doing so thanks for any help/tips you can offer!

OH< one more thing...why do I 'float' in SL? I just did a kneeling pose and I am floating in the air.

I have this same problem, so when I change something in my animation... Like setting the avvy a certain way, I always keep checking in the preview screen to make sure my elbows and wrist are not twisted, or that my hand it's really 2ft from my face instead of 2 inches.

See this thread.
I think there are differences among Poser AV, Preview AV, and In-World AV. Point must be that how your AV do animation in world. So you have to use your imagination and tweak it on Poser. If its hands are floating above its legs in world, you only have nothing but to bury its hands on its legs in Poser.

You need to move your hip down on Poser, too.

I'm using 'translate/pull' to pull the hips down into a sitting position and I was still floating. Is there another way I should be doing it? I also used the figure/drop to floor option.

move them lower, through the floor sometimes below it.

Didn't you touch your AV's "body"? Body's position would be ignored by BVH. If you pulled down its "body" 1m and its "hip" 0.5m, you would think and see your AV was 1.5m down on Poser, but actually just 0.5m down on SL.

Edit: I've tried to explain this by a picture, too.