It could be that you are not following two fundamental rules of cornering:
1) Looking deep into the turn: You can only know that your trajectory is one foot off if you are looking close in front of your bike.
2) One steering for the whole turn: You may be adjusting your steering along the turn in order to achieve your goal trajectory.
Think of the unintended consequences that you are creating if you are doing so, like diversion of attention, disorientation, over-stressing the front tire, etc.
The way I visualize cornering trajectory: to me it is like shooting a ball into the basketball hood from a distance, you feel the cross-wind, you estimate the distance and the angle, you gut-calculate the whole flight of the ball and then you impart your best directed push hoping for the best. Sometimes you miss for little and sometimes you nail it.
The hard mental, visual and calculation work in cornering happens prior the turn-in point, which is equivalent to the moment of actually pushing the ball. Let the bike "fly" describing that natural arc, free of unnecessary minute steering inputs and lean angle adjustments.
Missing an apex for 12 inches may add a few feet to the corner's total trajectory, which is not a big difference for a bike that moves 88 feet per second (60 mph). Distracting your attention from proper throttle control and from reference points and from spatial location may slow your bike much more.