lmin=0.3 is for AVG encoding above 2000kbit very good, but even with that you WONT get over 4000kbit
So ... the lmin just permits the encoder to do less quantisation on low bitrate parts of the movie, thats why on dark scenes less blocks (on DVD encodings at least) wont appear that fast.
But lower lmin values on lower AVG Bitrate encodings also cause tricky bahviours. That was figured out at a 1cd encoding Phil did .. as I remember. But maybe its all about the tricky 1pass which I dropped totally in case of mecoder! So at 2pass IMHO those tricky behaviours wont occur ... so try it by yourelf.