My brooks, for example, is raised at the back, dips and then raises at the front. I just bridge over the dip with the gauge. If your saddle is higher at the back than the front then I guess it'll be necessary to tilt it back a bit and see how you go, the power of the spirit level being you can keep a record of what you have done. You could either mark where the bubble is and write it down / photograph it, or put a spacer under the spirit level to get it level, and record that. I think the key is that using the spirit level you can have a recordable reference point that can then be tilted back / forward in small amounts to see how it works, so you have control and the ability to know how much its being changed each time. Hope all that makes sense!