The analog input range is 0V:4.096V. When using 3.3V as the voltage reference, that comes to about 0.82 maximum; when using 5V as the voltage reference, 20% of the turn will be clipped (and the rest will be noisy anyhow).
On the latest BelaMini RevC and Bela Cape RevC, a 4.096V voltage source is available on board (labelled REF and Vref respectively) and can be used instead of 3.3V if desired. Note: on BelaMini RevB the REF pin existed but needed an external buffer to be used. On RevC it can be used without external buffer.
As for the solution: rescale your input value!