Recently I played a 6500 point game vs mixed Beastmen and WoC. He brought two hellcanons and one of the shots scattered onto a unit of skirmishers and caused them to flee through some salamanders who then preceeded to flee through a unit of 42 saurus. The saurus failed the test and fled off the board. However, the saurus unit was within 12" of my Temple Guard unit with my slann in it, but they were not within 12" of the slann model. My opponent and I decided that I did not get the reroll because in the BRB it just says within 12". I was wondering if we decided correctly or incorrectly. On a more positive note, I did go on to win the game. The mvp's were definitely the ancient stegadons with sharp horns and Cowboys. The impact hits work wonders against anything. One charge on a tzeench sorcerer lord on a manticore with 1+ armour and 3+ reroll ward and both were gone. A unit of 8 minotaurs and a gore bull got totally wasted by a double charge with two of the stegs. They also had a huge psychological effect on my opponent. Once he realized how dangerous the impact hits were he tried to keep his skullcrushers and monsters away from them. This opened the unit of 8 skullcrushers up for a charge from my old blood cowboy. Who then got 3 overkill in the challenge and caused the skullcrushers to break and he overan them. Definitely the most critical points of the battle.
I believe you played it correctly for the exact reason you stated... a unit must be within 12" of the battle standard bearer in order to benefit from the "Hold Your Ground!" special rule.
Little bit of threadromancy here, but holy cow! How long did that battle take to complete? And gratz to the win of course.
We started playing at about 8 a.m. and finished at 9 p.m. (that includes breakfast, lunch, dinner, and bathroom breaks). So a total of 13 hours, most likely 10 without the breaks.