There may be a couple of reasons for remaining with the original thru- hull location:
-extra length of hose run for the
water pump to pull thru...this might cause too much depression at the
pump inlet....depression at the
pump inlet can cause impeller blades to flex too much resulting in early failure ( this happens with saildrives with blocked inlet slots)
-occasional possibility of sucking air if the stern lifts....if the hose gets too much air, the pump may loose its prime, especially if the impeller is a bit worn
- frequently debris such as weeds and
grass float on the surface but are less prevalent a foot or two under the surface....there is more chance of hose and strainer blockage with a pickup close to the surface
DougR