Hi Luca,
Thanks for contacting Syncfusion Support.
By default, in CrossHairBehaviour, we rounded the axis labels value as two decimals. However, we have achieved your requirement (displaying the small values in crosshair label) with the CustomCrossHairBehavior. We have prepared a demo sample for your reference and it can be downloaded from below link,
Please find the output screenshot,
Regards,
Devi