Hi!
I been flying R/C since 1975,both competing in pylonracing on an international level (been to USA on the Swedish pylonracing team in -95), scale and aircombat andflying helicopter and I can assure you that tank placement is very critical on every glow powered plane.
If you donīt belive me ; just mount the tank a few centimeters above the carb ...or below the carb and see what happens.