The accuracy of a .303 No.4 is a function of barrel harmonics and pressures imparted all along the long foreend. Just because there is one less point of contact in the complicated recipe of accuracy, doesn't necessarily mean one more opportunity for improvement.
The DCRA target shooters found that for a while a free-floated long-barreled Lee Enfield was the king at long range (800, 900, 1000 yds), better than all the competition. Something about barrel whip and flipping the action at the right vibration node to hammer the 147gr FMJ into the target. This situation disappeared when they switched to shooter-supplied 155gr ammunition and purpose built tubular receiver target rifles.
When testing across a broad sample of No.5's it is entirely possible that the short wood introduced an unexpected and unacceptible whip on a significant enough percentage of rifles. When 5% (or whatever it was) of trained soldiers can't hit their target due to rifle performance, that is reason for concern.
My 2 pence for what its worth.