Hi Tamadeez,
A small correction to your summary. A Radar altimeter does not receive its height information by the means of lasers but by the means of radar waves. A different, and higher, frequency wave than for example the VHF range used for communication. Radar altimeters normally only measure from 2500ft AGL. I am not sure however if the radar altimeter on the Q400 accounts for the gear height. Maybe Airline2Sim can clarify?
Cheers,
Jeroen