The first Southern E-6s were described in undated "EMC Proposition #00737", it referred to "EMC Specification #594-B". That was followed by four supplements dated October 2, November 29 and December 10, 1940 and January 10, 1941.* All of the SR passenger diesel specifications are in the SRHA archives at TVRM. Unfortunately, I'm just outside of Atlanta so I'll have to refer to the headlight description in the contemporary FT spec until I can check at the archives. (Photo attached)
EMD spec #606D (for FTs 6102-03 and B units 6154-55) describes "One headlight, EMD design, 14" diameter with multiple reflectors having seven (7) prefocused bulbs. How the "prefocused bulbs" were set above, below and to the left and right on the engine center line are not described.
The headlight changed with Supplement No.1 (May 19, 1944) to specification (FT-5400) for FTs 4103-06, 4112-17, 4303-05 and 4311-13. That describes "Each "A" unit to be equipped with a Pyle-National 250W, 32V headlight per endor's drawing #20-C-14590 MTP, EMD file reference #H-2.61, Pyle-National part #14590-EMS, with non glare reflector, less springs, studs, nuts, and washers, as a substitute to EMD standard 7-cluster headlight."
Notice that neither description answers David's question. More research can be done on how headlights were adjusted but given the length of an E unit carbody, we can assume no setting could compensate for undulations in the track or lighting around curves, one of the the reasons for oscillating headlights.
*EMC/EMD diesel orders began with a description (specification) of their standard product. If the purchasing railroad did not want any changes or customized features, the spec, as issued, described what would be delivered. To EMC/EMDs consternation, the Southern almost never accepted EMDs spec as written. (Electro Motive was interested in selling standardized units rather than complicate their production processes.) After negotiations with the purchasing railroad, a "Specification Supplement" would be issued to describe to changes.