im not sure where exactly i said to play a -2, but ill take your word for it :) i usually do play a - setting against a low 3 point shooting team, but this is a little twist on that - what about when the guards are still predominantly scoring?
there are a few things to consider. first, you are in a double edged sword situation, so any reasons you had to play your team at a default setting, now hold more water. for example, if i have a team i like to run a +2 with, i might still play a +2 or +1 against this kind of situation. if i had a team i played a -2 with by default, id definitely be playing a - setting against this situation.
second, the TYPE of guard scoring is important. is this a situation where the guards have good per, low lp, and the coach is just artificially holding them back? this is a major mistake by the coach, usually - but results in a lot of long range jump shots. in that case, a + setting still may be appropriate. on the other hand, if the team has a bunch of guards with mediocre per, and they have a bunch of lp and strong ath, you are probably seeing a team who just is not taking as many jumpers - and in that case, a - setting is definitely in order.
this does feel a bit like deja vu, so maybe i was asked this question specifically... i don't remember. but thats my thought on it.