Hi,
I found in the past never to under-estimate the power of reflected light.
I have my Phals on my living room (west-facing) mantle-piece: the room is quite large and has a bank of south facing windows and a pair of west facing windows. I keep the western window curtains drawn while the sun is on that side of the house and so the plants will never be in direct sun. However, the light from the south windows is enough to reflect off the cream coloured walls and create a nice light room all day. I guess what I'm trying to say is that, plants don't need to be right by a window in order to get light. Also, even though all the plants are in essentially the same place, they all have different leaf shades - so don't discount natural variation either.
(Oh, also on the subject of reflections, make sure that there's nothing shiny -like a surface or cd case or somthing- that will produce a reflection straight on to your plants and cause burn)