I have 4 pounds of external weight. was trying to avoid putting it on the tank straps but I guess I can try it. I have force fins and they are negative i think 10%
I, too, would be feet-heavy with an Al 80 if I placed my 4 lbs. of lead any lower than the upper camband. I don't think it's so unusual. When working out my optimal trim, my instructor had me put the 4 lbs. on my upper camband. Voila.