Piezo Z-probe with separate Z endstops - can't go bellow Z0
I have the following setup - large printer, so using two Zmin endstops with two Z stepper (MULTI_ZENDSTOP_HOMING) plus a Piezo probe (EXTRUDER_IS_Z_PROBE). Multi-Z homing works wonders. However, after Z homing, nozzle ends up few millimeters above bed and this is expected due to where the Z endstops are factory affixed to the chassis. This means that for the Z-probe to trigger, being a piezo probe integrated into the hotend assembly, we need to move Z bellow 0, in this case to around -4.3mm bellow. Mechanically this movement is possible - nothing is blocking, but I can not make the right settings to properly configure the firmware to do it (running on 1.04). G30 results in a short move in positive Z direction and a halt with a "Z probe failed" message.
Can you please guide me where to look and how is the right way to configure in this scenario? With Marlin I know how to do it, but I prefer Repetier all day, so would love to make it work with it. Thanks!