In OpenFHE, the same scaling factor is used for ciphertext-ciphertext and plaintext-ciphertext multiplications (for simplicity). This scaling factor is set using the scaleModSize variable in your example. Theoretically speaking, the scaling factor for plaintext-ciphertext multiplications can be set to a smaller number (by 10 bits or so) [if no ciphertext-ciphertext multiplications are performed at that level], but we use the same scaling factor (assuming the worst-case scenario). So the behavior you are describing is expected.
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