The lens is closest to the film when focused at infinity. At that point the center of most lenses is the distance f from the film. The center of the lens is usually about the plane of the diaphragm, except for telephoto designs where the “crossover” point falls forward of the diaphragm and, sometimes, forward of the entire lens.

The “crossover” point on a wide-angle lens may be somewhat displaced from the apparent center, but usually not by much.

The diaphragm generally is at the back of the shutter just forward of the front of the lens boardas mounted.

If you mount a flat lens board onto the camera and can place the front of the board at the distance f from the film plane, then you can focus at infinity without a recessed board.

If the design of the camera prevents placing the board at that position, then a recessed board is needed. Cambo cameras require a recessed board for lenses of about 100mm or shorter.

If the bellows can compress enough to let the board (or recessed board if necessary) reach the correct position, then a bag bellows isn’t need. Otherwise the bag bellows is needed.

For the camera you described the recessed board is probably necessary, but the bag bellows might be optional. By performing the above outlined distance test with your existing bellows and recessed lens board you can probably determine if the bag bellows are required.