A shallow approach might give a greater scatter in touchdown position, but a steep approach does not necessarily mean that it will be better, or that the aircraft will not float; this depends on how the flare and landing is flown (speed etc).
Touchdown scatter – long landings, can be a problem at LCY for some aircraft; a safety aid is the use of fixed distance markings / lights which identify the point by which touchdown should occur.
The 5.5 deg 10 approach at LCY was required for clearing obstacles (Canary Warf, and other buildings / cranes some of which have since been removed).
The 28 approach was designed to miss the river bridge – still not built; the 5.5 deg slope is retained because of the noise benefit.
BAe146 / Avro RJ operators can look up the difference in steep approach noise ratings in the AFM performance supplement.
The original approach angle at LCY was 7.5 deg, only usable by DHC-7 aircraft; this was primarily a ‘gimmick’ based on low environmental noise in order to get the airport approved.