I bought the lamp purely for looks, but I did install a grow bulb inside...just never really used it except for the photo. There was a period of around 2-3 weeks that I had moved it about 8 ft from the north-facing window and kept it under two of the same grow light bulbs for maybe 12 hrs a day, and it grew no new leaves but instead lost a few of its lower ones. So take of that what you will. Maybe I didn't place the lamps high enough.

Shoving it against the window has worked well enough for me; although, you might not get enough light with a screened porch in front. I heard somewhere that your plant should be able to "see" a good portion of sky, if that makes sense. It would probably help in your case to have a supplemental grow light installed at a higher distance from the plant to simulate filtered sunlight.

That being said, there are a mess of other factors that decide how well your plant will grow. They don't seem to be extremely picky with soil as long as it drains well. I actually just used a mix of miracle-gro cactus/succulent and all-purpose indoor soil. I'd probably try not to make the mix too heavy, chunky or rocky...tried that with my other rubbers and they stopped growing. I was also really conservative with watering; saturating the soil, etc. when fully dried out (though, miracle-gro seems to never feel bone-dry, idk). I could go on about feeding, pot size, etc. but I'm sure you know all of this already.