I have been examining the topography of the areas now held by the R+6 and IS in eastern Syria. There are not very good maps for this but the ones available on Google Earth and Google Maps are good enough. They show topographic terrain and the back roads.
I agree with TTG that the Tiger Forces Group under Suheil (the Stonewall of Syria) will be committed on the main axis of advance. Other axes will be used to fix the IS fighters in position making it nearly impossible for them to maneuver against the main axis of advance.
Possible axes of advance:
1. From possible positions east of al-tanf toward al bu kamal, and from al bu kamal north along the river road to deir al-zor. This advance will be opposed by IS forces in position to defend al bu kamal and the road north where the road runs through population centers held by IS and presumably fortified by them.
2. R+6 now hold the line of the ithria-rasafa highway. There is the possibility of advance to the east from the rasafa area to the Euphrates River and thence south along the west bank to deir- al-zor. This axis has the disadvantage of exposure of the left flank of the column and its line of supply to the SDF/YPG forces who at this point cannot be considered "friendly" by the R+6.
3. Straight forward from present positions on the Palmyra-sukhna- deir al zor highway. This has the disadvantage of being essentially a frontal attack on long emplaced IS forces. Some minor flanking attacks can be made by hooking left or right from the present line, but the approach is essentially frontal.
4. A close inspection of the terrain reveals that there are at least two hard surface roads that run SE from either side of ithriya to sukhna approaching sukhna from the NW. Employment of the Tiger Force Group on one or both of these roads would require them to move 80 miles or so to reach sukhna in a "turning movement" that will turn the enemy out of his present positions at sukhna and to the west where he is presently under severe pressure from R+6 forces east of Palmyra.
I used to do this kind of analysis for a living for US and allied forces as a "Planner" for the JCS. If I were asked my opinion I would recommend Couse Of Action 4 with supporting attacks on the other axes, But, commanders often are unwilling to accept advice and any damned thing could actually happen. pl