It took 2 hours to cook a pear cake. Recipe said 40-50 minutes. I used shelf 2 and conventional top and bottom heating, according to Bosch instruction book. However after 1 hour I changed in desperation to shelf 3 and 3D hot air. Cake turned out well, but far too long to cook correctly. What shelf should I use and what sort of heating? Oven is a double ovenHBN 43M 551 A