I also think 1/2tsp for 450gram flour is too little. It is possible to
use less yeast if the fermentation is longer. Maybe your recipe book
is not for bread machine.

The amount of yeast used in the recipe varies from brand to brand
slighly. The instruction from the yest manufacturers calls for too
much yeast. One sachet can be used for nearly 2lb flour. Besides, one
sachet is about 2.25 tsp yeast.
How about the recipe from the manual? You can start from that and
adjust it next time.