I do not believe the orientation of the mixer unit has anything to do with the pulsation problem.
The pump motor is activated by flow of water in the correct direction through a flow switch in the pump -- usually a pair of switches, one in the hot and one in the cold pipe, either of which turns on the pump.
Turning on the shower outlet valve usually allows sufficient flow to do this. If the flow falls below a certain rate the flow switch cuts out the motor. Raising the shower rose reduces the natural flow (due to reduced head of water). If your pressure is borderline anyway (cold water cistern only a bit higher than the shower rose) the flow can be so low when you turn on that the flow switch only just operates and starts the motor. But as soon as the pump starts to suck water via the pipework a slight partial vacuum occurs upstream of the pump. This causes a brief backflow of water in the wrong direction, which instantly deactivates the flow switch(es) and shuts off the pump.
The natural flow then restarts the pump which triggers the on/off cycle again, leading to pulsations.
Putting a non-return valve (single checkvalve) on the hot water outlet of the pump prevents these brief backflows, and so stops the pulsations. I'm not sure why you use the hot water outlet rather than the cold, but it may be because the hot supply usually has a lower flow/pressure due to longer pipework from cold water cistern to the pump.
The pump motor is activated by flow of water in the correct direction through a flow switch in the pump -- usually a pair of switches, one in the hot and one in the cold pipe, either of which turns on the pump.
Turning on the shower outlet valve usually allows sufficient flow to do this. If the flow falls below a certain rate the flow switch cuts out the motor. Raising the shower rose reduces the natural flow (due to reduced head of water). If your pressure is borderline anyway (cold water cistern only a bit higher than the shower rose) the flow can be so low when you turn on that the flow switch only just operates and starts the motor. But as soon as the pump starts to suck water via the pipework a slight partial vacuum occurs upstream of the pump. This causes a brief backflow of water in the wrong direction, which instantly deactivates the flow switch(es) and shuts off the pump.
The natural flow then restarts the pump which triggers the on/off cycle again, leading to pulsations.
Putting a non-return valve (single checkvalve) on the hot water outlet of the pump prevents these brief backflows, and so stops the pulsations. I'm not sure why you use the hot water outlet rather than the cold, but it may be because the hot supply usually has a lower flow/pressure due to longer pipework from cold water cistern to the pump.