Sigma fp L has a 61.0MP Full frame (36 x 24 mm ) sized BSI-CMOS sensor . On the other hand, Sony A7c has a 24.0MP Full frame (35.8 x 23.8 mm ) sized BSI-CMOS sensor and features Bionz X processor.
Sigma fp L's sensor provides 37MP more than Sony A7c's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the fp L and A7c sensor size comparison.
![Sigma fp L vs Sony A7c Sensor Size Comparison]()
Sensor Size and Resolution Comparison image of Sigma fp L and Sony A7c Cameras
Sigma fp L and Sony A7c have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.