Pump design vs Fluid dynamics

I've sparked a bit of a debate over here as I try to figure out the best way to plumb my 2 tier 3V system.

I understand there are a lot more experts and graduates floating around these forums, so for educational purposes, I'm bringing the discussion here in a hope that it will progress beyond supposition.

Basically what triggered this is that my pump lacked the power to pump through the HX and over to the boil kettle. While this will unlikely continue to be a problem with my new Chugger and underletting, rather than pumping over the top of the boiler, I'm still curious about the design principles.

It was suggested to place the HX coil on the input side of the pump, which would therefore reduce the pumping distance to the boiler. It has been stated that, given that the wort is traveling through the coil by gravity, that the pump is actually doing less work. However, it was counter-stated that despite gravity feed, the flow would be restricted and potentially cause cavitation.

Is anyone able to provide a more digestible conclusion as to whether or not the HX on the inlet side would ACTUALLY be a problem (rather than just potentially)?

Sorry, nothing empirical to offer, but from the various owner's manuals I've checked, restrictions are best placed on the outlet side of any impeller-driven beer pump...

Cheers!

Restrictions on the suction side of a pump will lower the pressure between the restriction (hx) and the pump whereas restrictions on the outlet will increase the pressure between the restriction and the pump. There are no problems with higher pressures, but cavitation will occur if the pressure drops too low. The pressure drop to create cavitation decreases as temperature increases until the boiling point where it is effectively cavitating with no pressure drop. Additionally, the gravitational effects will be the same whether traveling through a straight hose or a coil. However, the coil will add a restriction.

As mentioned, best practices would dictate that the suction piping be large diameter/ low restriction from the liquid source.

On the pump discharge side, some restriction from heat exchangers or throttling valves can be tolerated pretty well.

Pumps should be physically mounted lower than the outlet of the liquid source container.

Suction piping should be laid out as directly as practical with minimal horizontal runs and done so that the liquid would naturally drain toward the pump inlet port. Inlet port piping should contain no rises or traps that could air lock the pump.

Pump discharge piping should use the same philosophy, but will be a little more tolerant of air locking resulting from the piping layout.

Thanks for your responses, gentlemen. The only reasonable conclusion would be to place the HX after the outlet if at all possible. In my layout (as pictured), I can easily route or re-route the flow system anyway. The RED hose are the changes based on these recommendations. Cheers