Disclaimer: This is presenting fictitious opinions and does in no way, shape, or form encourage use nor condone the use of any illegal substances or the use of legal substances in an illegal manner. The information discussed is strictly for entertainment purposes and shall not take the place of qualified medical advice and should not be construed as an endorsement or recommendation for any illegal activity.
The hip operates in several planes of motion, the ankle ditto, the knee has only one motion. All the quad muscles insert into the patella so they have the same insertion point with slightly differing origins. This means that short of extreme positions that create lateral or medial shear at the knee (which you would notice and so would your surgeon's bank account) you can't preferentially load any of the quads.
That said the reason for multiple muscles is in the thigh is so that the thigh can perform different ROM and movement patterns. Physios are slowly coming to this conclusion after years of research and applied training in trying to isolate the VMO. The volume of work they have done in the face of their own belief of isolation is staggering and they are giving up on finding the panacea. I guaruntee that if you could isolate or even preferentially recruit the VL or VM then they would be having all ACL ruptured patients doing a specific width squat.
Now as to why you feel muscle X when doing Y width; how do you know that relatively speaking your form, depth, relative involvement of the other 4-5 knee flexors, relative involvement of the hip flexors, etc haven't changed? How do you know what your weak points are that are being compensated for?
Seriously; the bridge is already under offer, but the rock that keeps away tigers I've got in stock.