If your 2-3 and 3-4 shifts are OK one should be carefull of too much modulator reduction. Harsh shifts are better than sloppy ones (from the transmissions view point).
I would make as much as one turn counterclockwise on the modulator key. I also would first be sure that you are not shifting too late into second. The adjustment is to the control pressure cable and has a thumb wheel that can be reached without removing the aircleaner. You should try and make the shift earlier which will require lengthening the cable. The 190 has a screwy adjustment that is hard to see what you are doing but is easy once you get it. Since it is easier and might offer the best solution I would go there first.
Bosch Master, ASE Master, L1
33 years MB technician