SAGE is an end game strategy, similar to the nash equilibrium, for heads up play.
The one advantage of SAGE is that it is easy to memorize.
The downside, is that using SAGE against your average opponent is worse than using the simple strategy I'll outline here:
Take a look at the nash equilbrium. Ignore anything 8bb or above from the small blind (your strategy should be mixed at 8bb or above vs most players, meaning you open shove, limp, open fold or minraise some hands, therefore the nash charts nor SAGE applies). Below 8bb, you can often play "shove or fold" strategy from the small blind. However, the nash charts are not designed to exploit flaws in your opponent's strategy. Therefore, you'll want to deviate by default, as the average player is flawed (the avg player will call tighter than nash bb). So you should open jam wider than nash sb by default, to exploit the average opponent being too tight.
In the big blind, you're not deciding when you play shove or fold (if your opponent limps a button at 3bb, they're not jamming, if they're open jamming at 50bb every hand, they're playing the shove fold game), so you use the BB chart as a reference whenever your opponent is ONLY shoving or folding on their button (no limps, no minraises).
The average opponent will be open jamming tighter than nash sb, therefore, you should be calling tighter than nash bb.
Now, if you have information (reads) on what your opponent is doing, you should always adapt to that. If your opponent is open folding 90% of hands and jamming 10%, then you would not look at the chart or go to your default. My default strategy above is based on you having NO reads, and it is based on what the average person will do (readless strategy).
To develop specific "best" ranges against different opponent tendencies (ranges) from either blind, I'd recommend checking out programs such as ICMIZER, they're great when it comes to stuff like this.