Yes, I've said several times that there are actually fewer places than you'd think along the waterfront of Hull with access to deep water that are a) accessible and b) not covered by CCTV c) deserted enough so that no one would notice somebody disposing of a body. I suggested the area around the old St Andrew's Dock and the Lord Line building.
My feeling about LS being put into the River Hull higher up is that I suppose she could have somehow been carried by the current* (such as it is) right down past the TSB and The Deep and out into the estuary, but at other times, I look and I think... no. But then again like I said in a previous post, sometimes the simple explanation is the best.
I'm familiar with Hull, I was born there and lived there or environs (apart from three years at Uni) until I finally moved away in 1980.
*For those unfamiliar, it's not like the Seine in Paris or the Tiber in Rome where you have a large body of relatively swift moving water right in the heart of the city. It does divide the city neatly into East and West Hull, but at low tide sometimes its down to a trickle. Look at this picture of the former Hull trawler Arctic Corsair which is now moored up on the River Hull as a tourist attraction. This is at low tide, and you can see how little water is left - and this is quite a long way down towards the TSB and the confluence with the Humber.