One thing that often gets overlooked is that we do not actually have any real AASI samples. Because of this, AASI on G25 is usually estimated through what is essentially simulated coordinates. These AASI simulated coordinates are created by "subtracting" an assumed West Eurasian-related component from South Indian tribal populations or Indus Valley Periphery West on G25 PCA. However, this approach has several issues.
One issue is that the more subtraction is performed, the more artificial drift is introduced. This artificial drift makes the AASI simulation more susceptible to noise and instability. An AASI sim derived from Indus Periphery West samples where over 50 percent of its ancestry has been subtracted is likely to be noisy, for example it may produce small East Asian percentages that are not present in reality. Secondly, there is no certainty that the assumed West Eurasian proportions being removed, such as the exact percentages of Iran_N, ANE, ANF, CHG. etc are accurate because we also lack the perfect farmer proxy for IVC. If the way those proportions are removed does not perfectly reflect the true admixture, the results by using the AASI simulation can shift, particularly with the components that were subtracted.
Another important issue is that many of the AASI sims people rely on, including the one used by IllustrativeDNA, are generated from South Indian tribal groups. These populations are known to carry some level of Hoabinhian or divergent East Eurasian shift compared to most South Asians, which is not necessarily representative of the AASI component in most South Asian populations. When AASI simulations are derived from subtracting West Eurasian admix from South Indian tribals, that divergent East Eurasian shift that tribals carry will go over to the AASI sim. In distal models, such as IllustrativeDNA's HG & Farmer model, the pseudo Hoabinhian shift can cause the simulated AASI to absorb East Asian related ancestry and inflate AASI levels in certain populations (Pahadis, Nepalis, Bengalis, Kashmiris). AASI sims derived from tribal populations also affect other components. For example they inflate Iran_N and reduce ANF & Steppe MLBA proportions as the simulated "AASI South" contribution increases.
The best way to calculate proportions on G25 is actually through a proximal model such as IVCp+ Steppe MLBA + Ulladan (Ulladan because it doesn't have the pseudo-Hoabinhian shift like other tribals). The requirements are that you must know the AASI admixture proportions in certain IVC samples and tribal groups as estimated through qpAdm, and then indirectly calculate the value from there. Though if you really need, even an IVCp + Steppe MLBA + AASI sim model on G25 is preferable to using a HG & Farmer model with an AASI sim, as proximal models are more stable than distal modeling.