All ecu's interpolate all the time anyway, as the map only ever has a resolution of at most about 20*20, so its the only way it knows how much fuel to have at 23psi if you only have a value for 22 and 24 etc.

As you say though, thats a lot safer than having one value for 29+ and using it for everything.
But there is more to it than that, you can use TPS and RPM to effect it too of course, in which case the 29 at 7000rpm@100% throttle is only ever going to occur for a split second during spool up anyway, so you can live with that if you have a value suitable for the 32psi it ends up holding (just example figures)