Generally speaking you would bring it beyond the required line, to factor in some "spring back" but the amount depends on the wood and the length of heating time.
Bending a bow sideways is a nightmare, it's nothing like as easy as bending reflex/deflex/tips etc but with patience and a solid setup it's workable. Check out Del's blog, he has some excellent steam setups that work in situ so you don't have to dance around holding a hot lump of wood to get it from steam to clamps and have it cool down too much. With steam the key is speed - you have literally seconds before it cools down too much to work with.
One thing I've found works well is to steam, then clamp, then hit the hot area with a heat gun for a bit to blast some extra heat onto it. Minimises the risk of losing too much heat and the wood cracking under the clamp pressure.
Make certain you need to do all this though, as a bow that wobbles in and out of center is fine, it's only if the tips and dead center don't line up together that you have to move the bow with heat.