rusEfi trigger configuration is the most confusing part of rusEfi configuration unfortunately.
If rusEfi does not know your exact overall trigger shape and you use composite setup with crank sensor driving RPM and single tooth cam sensor providing phase information, that's considered "4 stroke without cam with VVT". Even if you do not have VVT :(
VVT mode 'first half'
This mode could be used for skipped-tooth wheels with single tooth cam sensors in order to support individual injection and coil-on-plug setups.
For example, 3/1 skipped wheel with cam sensor in the first half of the 720 cycle:
VVT mode 'second half'
Same as the above, but with CAM sensor indicating the second phase of 720 degree engine cycle.