Other diagrams I’ve seen either show a ‘flue collector’ that the flue rests on, holding it several inches above teh heat exchanger, of include a tab on the flue that I assume might keep the bottom of the flue opening several inches above the exchanger? This is a laars lite 175 model. I’ve just had to replace the exchanger and wonder if this may be part of the reason that it began leaking after only 6 years.