Because the oil coming from the pump to the filter, back in to the block, makes and vertical 90, then goes up then another 90 and then a 90 just to get to the mains.
I’m not sure where you’re going to pick up the oil to go into the front, but it will most likely have much less pressure drop than the oil coming from the main feed.
I only checked the pressure drop across the filter once and IIRC it was 8 or 10 PSI at 100 psi. So 110 in and 102 or 100 out. So I figured the pressure drop at the bearings was 20 psi or less.
I was also killing adjusters for a bit, and I was looking for solutions. One was putting direct oil into the shafts after the filter. Giant PITA and that didn’t fix the oil timing issue at the rockers.
What prompted that was I checked the pressure at the end of the shaft farthest from the feed (so the number 7 end on that side) and at a 40 psi hot idle there was only 10 psi at the end of the shaft. It was grabbing the bushing and that was why. If I had needle bearing rockers rockers that may have been ok. And I was killing adjusters.
The fix was get the idle pressure up to 60 hot and fix the oil timing issue to the adjusters. That stopped the adjuster eating and the higher line pressure kept the bushings off the shafts.