The shrinkage of sanding sealer is a much larger problem if it is put on in coats that are too thick or if recoated without allowing the previous coat to COMPLETELY dry.
Several thin properly dried coats are MUCH better than 2 thick coats.
I have been using Pactra Aero Gloss and Sig Sanding Sealer and Balsa Fillercoat dopes for over 30 years to finish balsa parts and the only time I have had problems with shrinkage is if it is applied too thick or not allowed adequate drying time between coats. Basically this is the same as with any color butyrate dope finish as well.

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