Battles of the late Third Age

[Tuor of Gondolin]

This is quite an interesting thread. As to maps covering areas of battles in Middle-earth, The Atlas of Middle-earth , by K. W. Fonstad, is useful.

The numbers in Saruman's army are interesting, and perhaps somewhat
inconsistent. It does seem probable that there were 6,000 + in the Battles of the Fords of Isen. So perhaps his withdrawal after killing Theodred was necessary to
regroup and reorganize, since he had just 10,000 + at Helm's Deep. And why
would a Rohirric rout in far western Rohan necessarily have been decisive, given that the basis of a 10, 000 + Rohan force still presumably existed in central and eastern Rohan, and you would think that a considerable portion could have been mustered in the Edoras/Dunharrow area.

Also, a military error is not necessarily the same as a mistake. An example is the failure of General Ewell at Gettysburg to attack Culp's Hill on July 1st. An attack might have taken it, but given the general situation as he knew it
he was probably right to regroup and attack the next day. Similarly, Saruman
and/or his commander (not elephant-man orc ) may have felt it both prudent and militarily correct to withdraw and regroup, although of course that did turn out to be an error.