Im confused now. From your initial question (unless I misunderstood it), it look as if you were wondering if your xr30 is enough coverage for your 42g Versa and if you should add a xr15 to the mix.
As for PAR, the specs on the xr304g is amazing. So I don't believe you would have a problem keeping sps. Most LED have the greatest par rating at the center and gradually decre9as away from the center. Your tank is narrow and not that much longer in terms of the coverage of a 24x24 spread that the xr30 is rated. So I think you are good in both coverage and part . As reef god [MENTION=2928]Tangwich[/MENTION], mentioned just have your coral placed closer the center than move out with less light demanding corals. However, theres more to keeping Sps then just light. Its a hodgepodge of things to keep inline and anything can go wrong..
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