At what point is the impeller damaged?

I have a 2007 Honda 50 4-stroke.

I usually flush it with fresh water on the muffs in the driveway.

Sometimes the pee stream is not strong on the muffs and I need to squeeze the cups together to create enough pressure for it to pee well. This usually happens when the motor is cold and goes away once it is up to temperature.

My question is: Does an impeller get damaged because no water is running through the motor (ie, not peeing yet) or because there is no water flowing against the inlet vents (ie, if you were to run it dry with no hose)?

Should I be worried about those moments when my hose is on and water is running against the inlet vents (but not strong enough to make it pee with strong flow) or is the impeller totally fine because it is being "bathed" in water?

Thanks.

There is a water intake under the cavitation plate.
try putting a piece of duct tape over it and see if that results in a better stream ?
I have fired my motor up by mistake while the leg was out of the water. (only for a few seconds)
with no damage done.

make sure you have full water pressure at the hose you are using before flushing.

Agree. What fries an impeller is rotating around the casting while dry.

I may opinon check wheter you have enough water
Pressure and if you have doubts that the impeller is old or broken
Buy a new one it very cheap check also if you have any
Water leaks from the pipe your using and also distance
If the water pipe is long will effect the pressure of water
Will be slow my opion