The maximum seabed slope on which bottom lock can be attained is highly dependent upon a number of different factors. Some examples include height difference between ranges (amplified difference if slope is steep and altitude on some beams is very low and others are high) and also backscatter properties based on incidence angle of the acoustic pulse on the sea floor.
An example statistic would be that at 10 m altitude, Syrinx will be able to track steep slopes of up to 75°. At very shallow altitude (1-2 m) the DVL would be able to track on a slope of 45°.