PA28 pilot is questioned by approach control for flying the DME arc transition between JIBTO and DUPNT on the GPS Runway 18 approach to IMM.

Narrative

I was flying IFR to IMM. I requested the GPS 18 approach at IMM but was already southwest of JIBTO (the IAF). I received vectors of a series of left turns back to JIBTO; followed by a clearance for the GPS 18 approach. I began flying the LBV 10 DME arc as depicted. The Controller stated I was 2 miles south of course and should correct. I responded the GPS showed I was on the arc and on course with the DME showing 9.9 miles from LBV. The Controller replied I was not supposed to be flying the arc and instead was supposed to be direct DUPNT (where the arc and the final approach course intersect). I proceeded direct DUPNT and completed the approach. After completing the flight; I contacted RSW Approach and spoke to the Controller; who stated he handled the flight about the confusing clearance. He stated that when more than a 90 degree vector (turn) was required for the aircraft to fly from present position over the IAF; then continue the approach flying a DME arc; the pilot was expected to pass over the IAF then direct to the next fix depicted (not via an arc). So he expected me to fly from JIBTO direct DUPNT. He stated that the FAA has clarified this policy 3-4 months ago at his facility. He stated that this policy was due to some aircraft not having equipment that can fly an arc if it is preceded by more than a 90 degree turn. Therefore; aircraft are expected to fly from point-to-point after passing the IAF if approaching the IAF from the angle my flight did. He was not able to explain what equipment limitations were. Although I was cleared for the approach; the Controller and I had a different understanding of how to transition from the IAF to the final approach course. In the future; I will confirm that the cleared routing is via the arc as depicted; especially if vectored from an unusual location (already past the IAF when beginning the approach).