Need help with aquascaping and SPS placement

[Ocypode sinensis]

Hi all, my 20 gallon mixed reef had been running 2 months and I'm still in the process of switch rockwork all around. It's one of those scapes that you can plug and switch those platform rocks around.

Question is:
Is my rockwork too tall? I have an XR15G6 Pro sitting 8" above it.
If I decided to get more Acropora (let see how the green slimer comes out), can I place it on top of those platforms, would it be too close to the surface of the water?
Also, how do you decide where does a coral goes, especially SPS? I'm too scared to glue them onto the rock but it makes them often times being moved around or just fell off the cranny i snug them into.

 

[Stephen8169301]

Love the scape why are you scared to glue down

 

[Ocypode sinensis]

Love the scape why are you scared to glue down

I might be overly anxious but I always fear that what if I glue a coral down and it doesn't like the flow/light

 

[CK00020]

Just pop it back off and remount

 

[Stephen8169301]

I might be overly anxious but I always fear that what if I glue a coral down and it doesn't like the flow/light

Yeah I hear ya. So put sps towards top prob new that glue down don’t like the spot? Just break off and pull out get old glue off and redo it just take your time no need to stress I’ve moved mine all over just be careful each spot has different intensities of light so just watch your corals for a week and make sure it’s happy