While that is slightly annoying im not sure how it can be coded and this should probably be reported/said/etc in the FIRS topic rather than a brand new one.
This is here in a separate and new thread quite appropriate:
Delivery to one industry and one industry only is an intrinsic behaviour of OpenTTD (and TTD, TTDPatch) and cannot be modified at all by NewGRFs. Stuff is alwas delivered to the industry accepting the cargo which lies closest to the station sign.
Can it be changed? Surely...
Will it improve gameplay? Not sure, maybe, maybe not and probably depends. You might then have many industries which produce less instead of one which produces loads.