Yep, the throws can't be supposed to always hit the broom.
As far as my experience goes every shot can be slightly off on broom, witch is the realistic way for it to be. However. On full weight shots, a hair more precision would have been a change to the better. Every other shot is half a rock off the broom, witch is supposed to be a much rarer occurrence, possibly 1 in 10, tho most shots will be missed by an inch or three.
Moreover, what bugs me alot more is the fact the full weight shots aren't really hard at all. It's virtually impossible to throw a double peal and roll the shooter out. To be realistic a full powered shot can take get 4 or even 5 rocks out of play. Secondly the forward roll after impact ought to be removed. Thirdly friction in-between rocks is too low. A thin hit should cause a much flatter angle.