Sorry I'm a little late on this one and Im glad you got it sorted...I am a manager of a scaffolding company in Sheffield, unfortunalty you must have had a scaffolder who thought about what was easiest for him rather than letting common sense prevail. There is no minimumn height for a lift, however the scaffolding company (Legally) should have prepared a Risk Assessment for their operatives and client which should have identified this obvious Hazard and the Control Measure would be to ensure the base lift was above the entrance or the entrance was isolated...sorry to bore!!
In the good old days when I was on the tools the bottom lift on a street job was always set to the top of a bobbys hat!! We had a particular bobby in Nottingham in the early 80's who was 6'10 so you can imagine we built the bottom lift with the help of milk crates!!