The software bed leveling is applied as the gcode is being streamed to the printer. You can always check that it is working by opening the G-Code Terminal and looking at the commands that are being sent. Typically, G1 commands will not have Z values since the printer does not do a lot of moving up and down. Here is an example.
->N13285 G1 Y-2.48 E729.58*27 [1057.989]
->N13286 M105*41 [1058.161]
<-ok T:254.9 /255.0 @200 B:75.0 /75.0 @66 [1058.162]
->N13287 G1 Y2.12 E729.733*1 [1058.162]
->N13288 G1 Y6.72 E729.886*13 [1058.194]
However, if software leveling is being applied then all of the G1 commands will have a Z value, since the printer will be constantly moving up and down to compensate for the leveling.
->N1162 G1 X-10 Y-31.1 Z1.392 E10.191*47 [447.868]
->N1163 G1 X-8.91 Y-31.4 Z1.396 E10.253*61 [447.925]
->N1164 G1 X-7.81 Y-31.69 Z1.4 E10.314*5 [447.982]
->N1165 G1 X-6.72 Y-31.98 Z1.404 E10.375*4 [448.039]