Lighting Help - 24" or 36" on 36x24x16 tank

I was all set on getting 6 bulb 36" T5 fixture....then started seeing quite a few videos on 'light spillage'.  Started thinking about a 24" 6 bulb fixture.  I was thinking 6 bulbs to cover the 24" width...and then 24" fixture - if suspended 6-8" above tank would provide enough spread to cover the 3' length of tank - and since the tank is only 16" deep - should still have enough light/par to grow SPS.  Any reefers want to chime in on their input?