have you ever tried using 2*HPS + 1*MH for flower?
I used to every now and then back in the 80s, but after they came out with the Hortilux HPS with some Blue added, I stopped using the combination. I used 2 MH, and 1 HPS. Also consider if both lights cover a 4 x 4, and I have a light every 4 feet the light in the middle is giving very little added spectrum to the plants on each side. At that rate it would be best to have a 600w MH, and a 600w HPS in one fixture.
The Hortilux HPS has considerably more umol vs the MH. I used 1000w MH from78-the mid 90s, and switched to the Hortilux HPS when they added Blue.
I got better results with the Hortilux as a single source, so I didnt really see a need to combine them. I know people that have, and they have a good outcome.