Here are the various medical parking areas, as well as other useful information.
Epcot is first few rows closest to entrance. It is not much further than where the trams let people off. Normally the remainder of the sections where the medical parking is do not have tram stops as they are so close.
Studio they are the first few rows. They are closer to the entrance than anything except the trams themselves and the Disney buses. Note that non-Disney buses park further than medical parking.
Animal Kingdom always stay to the right (follow the blue line) after you pass through the toll plaza. The medical parking is the closest parking to the entrance; it is about the same distance as the tram loading area.
Magic Kingdom is the most difficult. If you can use the Disney buses, they let you off very close to the actual park entrance. If you are looking for medical parking, it is at the very front of the TTC lot. However, you then have to go on the sidewalk through an underpass where the trams also go and pass the kennels. Once you have gone through the TTC gate, you are much better off using the fery boats rather than the monorail, as the ramp to the monorail is very steep and pushing or self-wheeling can be very difficult.
Note also that if you go to any of the deluxe hotels ( Animal Kingdom, Boardwalk, Contemporary, Grand Floridian, Polynesian, Wilderness or Y&B) there is no charge for valet parking with a disability hang tag. HOWEVER the valets are "tip positions" and they do not get any of the fee which is normally charged. I will normally tip $2.00 both when dropping off the car as well as when picking it up if I do not need assistance with the
ECV. Since I use an ECV (but not always) if the valet will handle loading/unloading and assembly/disassembly of the ECV I will tip $5.00 instead of $2.00. (Note if I have the ECV and do not get assistance, not only will there be no tip, but also a discussion with a supervisor.) In your case, if the valet also loads or unloads the wheelchair I would suggest a tip largef than $2.00 but not as high as the $5.00 as an ECV is both heavier and more complex than a wheelchair.