U90 TRACON Controller reported a flight crew misinterpreted the minimum descent altitude of an approach segment to TUS which resulted in a low altitude alert and CFTT event. Controller stated the procedure seems to be causing some confusion among pilots.

Narrative

I had relieved the previous Controller who had cleared Aircraft X for the RNAV/GPS-Z to runway 29R. Aircraft X was descending on the approach from JOKIM to the next waypoint VEDTU. The published altitude for the approach between JOKIM and VEDTU is 7800 ft. I observed Aircraft X at 7500 ft. and they appeared to not be at VEDTU yet. I pulled up the map for the RNAV/GPS-Z for 29R and Aircraft X was approximately 3 miles from VEDTU now at 7400 ft. I issued a low altitude alert to Aircraft X advising of the MDA (Minimum Descent Altitude) being 7800 ft. for the segment of the approach. Aircraft X began to level at approximately 7000 ft.; and I asked Aircraft X if they had the terrain in sight. They replied in the affirmative. At this point they were over VEDTU and on the next segment of the approach that allows descent to 5300 ft. I asked Aircraft X if they wanted to be broken off the approach and climbed or if they wanted to continue. They stated they wanted to continue the approach. I advised Aircraft X that the MDA for the segment from VEDTU to ATOGE was 5300 ft. They had stated they 'see that now'. I did not issue a climb to Aircraft X because the terrain in the area is well below the published altitudes and they were in a 7200 ft. MVA (Minimum Vectoring Altitude) when they were at 7400 ft.This approach plate seems to be confusing to pilots. This descent to a lower altitude than published on that segment of the approach happens fairly often as of late. If there is a way to make the altitude more clear to pilots for each segment that would be beneficial. As of right now there is a small '7800' just over the leg between VEDTU and JOKIM. The profile view only references ATOGE at 5300 ft. Some way to draw attention to the step down fixes on the approach I believe would help pilots.