pump placement?

After reading your other thread about this, I have to admit that I am confused.

If I am understanding it correctly, I believe the answer to your question is:

Yes, it does matter. and

No, that is not a good pump placement.

Please explain your proposed setup in more detail so that we can help you avoid mistakes.

Centrifugal pumps like to have a net positive inlet head pressure and they are less prone to cavitation if the inlet head (pressure) is positive. In other words if the inlet of the pump is above the water line you would likely have to prime it to produce flow (not all pumps). Under a suction the pressure of the water is lower and can react by flashing to steam (albeit small). This flash then causes small bubbles to appear in the water stream which can cause the pump to stall and then the prime is lost. Under extreme circumstances these small bubbles act like rocks on the impeller and can cause it to disintegrate.

This little phenom is more of a concern on high pressure high flow pumps so this is not as big of a deal as I have made it sound.  The  bottom line is that it is better to have the pump inlet below the water line as much as possible.