Just did a bunch of testing with combos from mixups into mid mines for the proper spacing. All assume the mine is already out. In order from swag to damage. xx = cancel into
b13 xx LV2 db1, mine hits, db1 hits, 1 xx MB db2, b3, j3, u3 xx db2 46%
b13 xx probe, mine hits, walk forward slightly, u3 xx bf2, probe hits, u3 xx MB db2, b3, forward dash, u3 xx db2 46% *Forward walk to make sure u3 connects. Side switching may occur after the corp charge.
d3, mine hits, dash forward, f2 xx MB db2, b3, j3, u3 xx db2 51%
f2, dash forward, mine hits, j3, b2 xx MB db2, b3, j2, u3 xx db2 53% * Not recommended since it's really spacing-dependent.
EDIT: Suggested combo: f2, mine hits, dash forward, f2 xx MB db2, b3, j2, 21 xx db2 48%
b13, mine hits, slight wait, j3, f2 xx MB db2, b3, j3, u3 xx db2 53% *Wait to prevent crossup after the first j3.
b2u3, mine hits, slight wait, j3, b2 xx MB db2, b3, j2, u3 xx db2 56% *Wait to hit j3 on the way down as the opponent pops up. *f2 xx MB db2 works on big characters like Doomsday and Bane.
b2u3d3, mine hits, f2 xx MB db2, b3, j2, u3 xx db2 58% *Has to be a far mine on big characters like Bane and Doomsday.
b13, mine hits, slight wait, j3, f2 xx MB db2, fj2, 22 xx MB b3, j3, u3 xx db2 62% *Wait to prevent crossup after the first j3.
b2u3, mine hits, slight wait, j3, b2 xx MB db2, fj2, 22 xx MB b3, j2, u3 xx db2 65% *Wait to hit j3 on the way down as the opponent pops up. f2 xx MB db2 works on big characters like Doomsday and Bane.
b2u3d3, mine hits, f2 xx MB db2, fj2, 22 xx MB B3, j2, walk forward very slightly u3 xx db2 67% *Without the walk forward the combo is inconsistent. Has to be a far mine on big characters like Bane and Doomsday.
In general I recommend ending all of these with string xx bf2 since it allows for more setups. db2 leaves Lex at disadvantage if tech rolled and can be punished by 5framez fullscreen and moves that impact on the 17th frame or faster in the corner. b2u3d3 and b13 are both hit-confirmable so mastering them will make his mixups completely safe under normal circumstances.
EDIT: db2 is less disadvantage on hit when done with some space between Lex and the opponent. With space it's completely safe midscreen. In the corner it's always punishable.