can make change to the yolov5 backbone ?

[alkhalisy]

Dear, I try to remove P3 and P5 detection and still tp P4, and I do require a change in the Neck, and everything becomes well and works. When I try to delete C5 from the feature Extraction Backbone and do modifications in the neck, the error happened
"File "/content/yolov5/models/yolo.py", line 334, in
args.append([ch[x] for x in f])
IndexError: list index out of range"
why any I can not do any change to the backbone???

nc: 80 # number of classes
depth_multiple: 0.33 # model depth multiple
width_multiple: 0.50 # layer channel multiple
anchors:

[30,61, 62,45, 59,119] # P4/16
backbone:

[[-1, 1, Conv, [64, 6, 2, 2]], # 0-P1/2
[-1, 1, Conv, [128, 3, 2]], # 1-P2/4
[-1, 3, C3, [128]],
[-1, 1, Conv, [256, 3, 2]], # 3-P3/8
[-1, 3, C3, [256]],
[-1, 1, Conv, [512, 3, 2]], # 5-P4/16
[-1, 3, C3, [512]],
[-1, 1, SPPF, [512, 5]], # 9
]

head:
[
[[-1, 6], 1, Concat, [1]], # cat backbone P4
[-1, 3, C3, [512, False]], # 13

[-1, 1, Conv, [256, 1, 1]],
[-1, 1, nn.Upsample, [None, 2, 'nearest']],
[[-1, 4], 1, Concat, [1]], # cat backbone P3
[-1, 3, C3, [256, False]], # 17 (P3/8-small)

[-1, 1, Conv, [256, 3, 2]],
[[-1, 14], 1, Concat, [1]], # cat head P4
[-1, 3, C3, [512, False]], # 20 (P4/16-medium)

[[20], 1, Detect, [nc, anchors]], # Detect( P4)
]