I'm not running Platinums, but most footprints are similar, and yeah, I'd be a bit concerned about 8 inches. I'm running 1000 watts in a 4x4 and I like to keep 'em at least a foot away.
I've developed the habit of running a ton of light over my vegging plants, starting with a CFL rig that ran 135 watts per plant. So I always get very tight nodes, sometimes 2 per inch. That helps keep them short while they're maturing.
If I flip plants with 8-12 tops at 12-14 inches tall, they almost always finish around 25 inches. And I run sativas and sativa doms. A nice thick plant flipped at 12 inches should be safe.
[Edit] And I once harvested 3+ ounces from a 20 inch plant.
I've developed the habit of running a ton of light over my vegging plants, starting with a CFL rig that ran 135 watts per plant. So I always get very tight nodes, sometimes 2 per inch. That helps keep them short while they're maturing.
If I flip plants with 8-12 tops at 12-14 inches tall, they almost always finish around 25 inches. And I run sativas and sativa doms. A nice thick plant flipped at 12 inches should be safe.
[Edit] And I once harvested 3+ ounces from a 20 inch plant.