Time Aligning Questions

Hello All,
Regarding biamped MTM designs, which approach is better -
A stepped front baffle, or
a flat baffle and the tweeter delayed, and if delayed,
what passive or line level delay circuit approach is best.

Has anybody tried mounting a modern car audio surface mounting pod tweeter in front of a
suitable say 5" or 6 1/2", ala old car coaxial designs, and passively or actively delaying the tweeter ?.

Eric.