# How to change the point name of second $x$ axis in 2D plot?

This example was already previously investigated in this website (A 2D-plot with second X-axis) but I want to know little bit more about that. The code is as follows. Plot has two $$x$$ axis. In the upper $$x$$ axis, how can I display the point $$\frac{\pi}{2}$$ as 1 and $$\frac{3 \pi}{2}$$ as 2. But it should not reflect on other axis. I just want to display the points mentioned at upper $$x$$- axis with different numbers.

npi2 = {π/2, 3 π/2};
npi3 = {π/3, 2 π/3, 4 π/3, 5 π/3};
npi4 = {π/4, 3 π/4, 5 π/4, 7 π/4};
Plot[Sin[x]^2 Cos[x], {x, 0, 2 π}, Frame -> True,
FrameTicks -> {{Automatic, npi3}, {npi4, npi2}}]


npi2 = Transpose[{{π/2, 3 π/2}, {1, 2}}];