The optium light from the 150 hps is a 14 in sphere around the light.
If you put her in the middle it should cover most of the canopy with good light.
But it would be a bit dark around the edges.
MY cab is about the same size an i went with a 175 Mh an a 150 Hps. Sealed an vented the top with the lights to control heat.
I got 45 day old plant in my cab with 9-10 nodes wraping aournd my buckets edge, only 5-6 in tall.
Keep em close to the lights an they wont stretch tell flower. I like growning leafs an buds not stems.
Training helps even more.
You can keep em low.