Pilot reported confused wording and ATC intent of the SFF airport Felts Four Departure resulting in a pilot deviation to avoid traffic.

Narrative

On departure from SFF Runway 22R on the FELTS4 we were passing through 5500 ft. and I made a turn to the left under the impression there may be a traffic conflict due to the lack of an expected ATC vector. I observed traffic converging on TCAS and visually but then lost visual contact with the traffic. This led to my aircraft turning toward the traffic rather than away from the traffic. After realizing this I turned back to the right slightly then back to the left and increased my climb rate. The traffic passed under me with a separation of over 1;000 feet within approximately 3 miles without causing a TA alert. At the time I was not aware that the traffic I was attempting to avoid was IFR also. Upon turning I immediately advised ATC that I was turning for traffic but was probably not clear about my concern and inquired if they would like me to turn for this traffic ahead.The problem appeared to be a misunderstanding of the published departure procedure; FELTS4.I reviewed the departure procedure on the ground prior to taxi and while my initial cleared altitude was 12;000 feet the departure procedure appeared to require an initial turn to a heading of 190 and then terminate at 5;500 feet.A subsequent review of the departure procedure led me to believe my initial understanding of the procedure was incorrect. I was confused about the design of the procedure and realized it didn't make sense to me.After a discussion with the Spokane ATC on the telephone and an explanation of my initial understanding of the procedure and my concern about not receiving a vector prior to reaching 5;500 feet the Controller agreed that the departure procedure was confusing and stated that it was a common source of pilot deviations and would like to see it changed to eliminate the confusion.Even after the discussion with ATC I am still unsure of the reason why there is an altitude limit on the departure of 5;500 feet for the Runway 22R procedure and find it to be a confusing procedure. ATC is expecting all aircraft to maintain the departure heading to 12;000 feet; not 5;500 feet despite the procedure stating to maintain the heading to 5;500 feet.I feel the unusual nature of the departure procedure is a hazard to pilots and may cause them to either stop climbing at 5;500 feet or feel they've reached the end of the procedure similar to an obstacle departure procedure or a procedure that requires a climb to a specified altitude and then a turn. My concern that this is a hazard was confirmed during my discussion with ATC who stated that this is a common misconception. There doesn't seem to be any reason why the altitude limit is listed at all except for lost comms to prevent an early turn toward terrain but if this is the case this should be specified.Because the aircraft is managed under a lease with an operator under 14 CFR 135 and I am the Chief Pilot I will list this airport as a hazard in our safety management system (SMS) so that other flight crews can identify the hazard and mitigate the risk. Our procedures allow us to identify specific hazards to alert crews. This will not help pilots from other organizations; however and I still feel the procedure should be revised to clarify the intent of the procedure.