I noticed that when I read about fiscal policy and the AD-AS model, it looks implicitly assumed that when we use fiscal policy we intend to shift the AD, even when the economy experienced a negative supply shock. And even considering that fiscal policy can influence the SRAS too (like decreased taxes on businesses and increased government spending on infrastructure can decrease costs for businesses).
But why? Why don't we talk about using fiscal policy to shift the SRAS? I suspect that it's because in the AD-AS model any fiscal policy shifts the AD much more significantly than the SRAS. Is my guess correct?