This might sound very obvious, but aren't yokomen uchi and shomen uchi very much stylised attacks, representative of a number of possible techniques?
Yokomen uchi could well be substituted for a hook punch or hammer fist, or other similar roundhouse style technique. As the technique is representative of many different possible attacks, wouldn't it be reasonable to assume that the line of attack could also significantly vary?
Another important point I find with yokomen is how nage moves. If nage tries to blend too early, I certainly step off line to redirect my attack and keep on target for their neck