Getting your raise size correct at various stages in a tournament is an important aspect to successful play. Basically the later on the tournament you get, the shallower your standard raise should become (obv as a general rule, not in all instances).
As you start to get deep 2.5 times the big blind or less is perfectly fine. Many players will not call to even a small raise, at this point, unless they have a half-decent hand. So it enables you to pick up pots very cheaply. With the antes on offer as well, this makes each hand a very desirable pot.
The shallow pre-flop raise like this also gives you more room to either fold cheaply, or to evaluate any raise/push to see if there is value there for you.
We can illustrate with an example. Here, poker pro Jon Turner (PearlJammed) is deep in a tournament, and raises to his standard for the blind level, 4875. This is 2.4375 times the big blind. With the antes, there is a 5000 chip gain here on offer if the opponents fold, which they do in this example. Very much low risk for high gain, compared to a std 3xBB raise before the antes.
Full Tilt Poker Game #6468631057: FTOPS Event #21 (47445419), Table 15 - 1000/2000 Ante 250 - No Limit Hold’em - 16:33:39 ET - 2008/05/18
Seat 1: binrich (25,064)
Seat 3: ckingusc (49,646)
Seat 4: 747wd (72,740)
Seat 5: PearlJammed (109,613)
Seat 6: lilfishy897 (196,251)
Seat 7: rrrobins (199,538)
Seat 8: Erich Kollmann (93,315)
Seat 9: I_Do_Goats (172,888)
binrich antes 250
ckingusc antes 250
747wd antes 250
PearlJammed antes 250
lilfishy897 antes 250
rrrobins antes 250
Erich Kollmann antes 250
I_Do_Goats antes 250
I_Do_Goats posts the small blind of 1,000
binrich posts the big blind of 2,000
The button is in seat #8
*** HOLE CARDS ***
ckingusc folds
747wd folds
PearlJammed raises to 4,875
lilfishy897 folds
rrrobins folds
Erich Kollmann folds
I_Do_Goats folds
binrich folds
Uncalled bet of 2,875 returned to PearlJammed
PearlJammed mucks
PearlJammed wins the pot (7,000)
*** SUMMARY ***
Total pot 7,000 | Rake 0
Seat 1: binrich (big blind) folded before the Flop
Seat 3: ckingusc folded before the Flop
Seat 4: 747wd folded before the Flop
Seat 5: PearlJammed collected (7,000), mucked
Seat 6: lilfishy897 folded before the Flop
Seat 7: rrrobins folded before the Flop
Seat 8: Erich Kollmann (button) folded before the Flop
Seat 9: I_Do_Goats (small blind) folded before the Flop