A total of 2 reviews of this product on Reddit.
There should be an indent for the chin to go down..the ones the chiro/physio make have it so the tie is below the chin so you can still bring your chin to chest. This is the one I use…2″ height is plenty and I turn it around so the tie is at the front
Bilt-Rite Mastex Health 2 Inch Cervical Foam Collar, Beige https://www.amazon.ca/dp/B00KCEG3A0/ref=cm_sw_r_apan_i_CP9EXRBKASRFNHFH9VAF
You might try one of those soft foam cervical collars like https://www.amazon.com/Bilt-Rite-Mastex-Health-Cervical-Collar/dp/B00KCEG3A0/ref=sr_1_17?keywords=Cervical+collar&qid=1639354384&sr=8-17
If you can get it to fit under your jacket collar it there shouldn’t be a way for a blade to slide under it and it goes up pretty high. Not much protection against penetration from a broken blade but might suffice against impact from tips.