Floor nailer nailing too deep. Am I even using the right tool?
These nailers are made to handle solid wood flooring and thick subfloors.  Your engineered floor is much easier to nail, and you may have a pretty "soft" subfloor as well (not a bad thing, necessarily, just saying that it accepts nails pretty easily).  The max PSI is important because that is the MOST the tool can handle without blowing seals, etc.  

Don't pay attention to the minimum.  On nailers, that is a "best guess" for the PSI needed to do a typical job so you can make sure the compressor you have will be enough.  It's not like you will hurt the nailer with low pressure.  A nailer might work down to 10PSI if you are nailing styrofoam (not that you would want to do that).

So, play with the pressure until it's driving the staples the correct depth.  However, when you use a lower pressure like that, any irregularity in the subfloor will lead to a staple that's not driven all the way.  That's fine - just be prepared to manually set a staple every once in a while and don't get frustrated when it happens.  Find the sweet spot on pressure and even adjust it if you get to a section of floor that starts behaving differently.