Leaf Blowers

I have the 125 BV. It is a wonderful little blower vac. When using the vacuum mulch feature, the air flow to the bag is choked off so there is not a good air flow to the bag, and material backs up in the vacuum tube. I have watched the You Tube video and it is not clear how on is expected to hold the unit with two hands and with the bag supported over the shoulder, in a position to achieve good air flow to the bag. I thought if I shortened the strap it would have better flow, except that the strap is already as short is it can be.