So Im street tuning my fc with a microtech lt10c currently at 20psi but I noticed that the boost drops off to about 15psi at redline, the engine has all the supporting mods to hold the power, the car with the previous owner was running an old haltech f9 at 30psi (street/drag car) but I changed the ecu so cant really remember if it did this in the past or not... any tips? its throwing off my tune it leans a little at high rpm because of this, its running an emusa 2bolt wastegate and air regulator valve for boost control the turbo I really dont know the specs its not too big the compressor side is .70 a/r and the turbine side is .96a/r t4 full 3 inch exhaust

 

Need compressor specs of turbo, could just be out of flow so boost drops.

On my old T04B with smaller HiFi compressor housing it would only flow enough for ~380rwhp. I got my set-up optimized to where that was down at 14-16psi (no air filter on end of velocity stack vs airfilter on stack).
Then tuned rich and retarded in high rpm for antilag basically and oversped compressor up to 18psi boost, but it only made peak 383rwhp LOL (though up to 20hp more under the curve.)

 

I honestly dont know the specifics about the turbo, but I guess is some sort off t04s by the looks of it, also I'm still running the stock tmic here is a pic of the turbo

 

You could run your wastegate signal line to your UIM or somewhere post intercooler. Running your wastegate line to your compressor housing that is seeing extreme temperatures in the upper RPMs can play a role in the wastegate seeing a high pressure reading and opening the gate more. Whereas your MAP sensor/boost gauge is likely on the colder side... Doing this simple change fixed my boost fall off on my mustang. Something to think about.