Problem fitting a shower screen

[motah33]

We're trying to fit a show screen which requires two brackets to be fitted on the tiles at the side of the bath (this is a for a shower from a mixer tap). The problem is that each bracket requires two holes, and the bottom bracket sits flush with the bath itself - we can't get the drill to make the hole because the chuck on the drill hits the top of the bath and so the hole will be too high.
The other solution is to make a hole at an angle but I don't know if this is a good idea.

The other solution seems to be to move the bracket further up the wall so the drill can make the bottom most hole for the bracket. These holes are made through the tiles. The problem here is that plastic guard that goes at the bottom of the glass screen may not reach the top of the bath, therefore leaving a nice gap between the plastic shield and the top of the bath.

Any ideas of how to get around this? Thanks.