I don't think it's a problem with "contact" vs "contact & influence" but a problem with depth.
As examples, for me to get a keel shot on a large old passenger carrier (draft 28.0 feet), I set the depth for 24, and on a huge European liner (draft 27.9 feet), I have to set the depth at 20!
You may just need to experiment to find some useable depths rather than using the apparently useless drafts listed in the recognition manual.
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