You shouldn't worry about how far the tank is from boiler as long as the tank is higher then the burner on boiler. I would however agree about the tigerloop, it is a clever device and easy to fit, which uses a series of chambers to create a vacum that pulls your oil from tank even if tank is lower then burner. The best thing about it is when you run out of oil there is no need to bleed line as tigerloop does this automatically and restores vacum, handy bit of kit and probably not that expensive!