I think it depends on the size of your vessel and the volume that you brew - i dont see the heating element being much of a factor. For me, I generally brew 10 gallon batches, but occasionally i brew 5 gallon batches as well. So for me, i ended up putting the whirlpool inlet at about the 5 gallon mark, pointed slightly up. This way when the 5 gallon batch is complete and i have roughly 6 gallons of wort in the kettle my whirlpool inlet is still submerged. Likewise for 10 gallon it is completely submerged but due to it pointing upwards i still get a good whirlpool going. I could have also put the inlet at around the 8 gallon mark pointed down and achieved the same balance between the two volumes.