i think the market in this case may have responded far more quickly due to the timing of the goal (11th minute). i reckon you may have to split up your bets into timebands to attempt to catch the perceived value across the various timebands of the game. i'd think in 10 minute segments and try to determine fair value on a goal being scored inside any of these segments. of course, if there's a LOT of activity, that will naturally increase the unders odds. in short, this rule is such a basic starter that i feel you'll need to invest your energy in identifying the nuances of the games that you feel will qualify for this rule.
if it's any consolation, i have a couple of rules that are only SAFE to apply to games that have a very tightly bound balance on the odds ahead of the start of the game. you may do well to start from that position in determining how to build this up further. trust me, you MAY stumble upon a balance of odds where the rule works for 90% of the games that you actively identify - however, it does need this spadework up front first to get under the skin of the intention.
pun definitely intended (in this game anyway

) -you need to find the platitudes
[edit] interestingly, the 2nd goal came at the 81st minute mark. *occassionally* (

) in a *busy* game, this 72-80 minute mark can produce a fairly decent opportunity, IF the activity has ramped up after half time.. this may be another angle to look at!