It is that - I've tried it!
The "record only in HD" does not force it to record from an HD channel. It only records an episode with the "HD' marker next to the episode details.
The OP has "Record only in HD" set in their posted image.
Like the "only record NEW" episodes is nothing to do with the NEW flag - it is based on other metadata.
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V6 TiVo (with MRS & UHD/HDR)
VIVID 500 (500/35mb) in Area 31
SkyQ Silver Bundle (UHD + 2 minis)