38kV to 208V Voltage drop

am designing a 38kV transmission system that feeds delta wye transformers at from 2500kVA to 150kVA in the USA. When I enter all of the data into SKM and perform the load flow and Voltage drop calculations the combined votlage drop from the point of connection to the secondary of the low voltage transformer total 6-8%.

Q1) The NEC requires the voltage drop to be limited to 5%, but I am at the transmission level - are there any standars that govern the higher voltage levels?

Q2) To prevent my calculations from showing such a high voltage drop is it customary practice to utilize the transformer taps in the SKM project. How else can this be fixed?

Q3) Typically do voltage drop calculations restart at the secondary of the transformer?