You do have a big challenge. Heat stress will cause increased HR drift. Since you live there you are well acclimated already so that’s not an issue. We have clients in India and other hot climates who all report the same thing. This might explain why there are not many elite distance runners coming out of the equatorial countries. It is just much harder to accumulate the easy distance need to build basic aerobic capacity.
My recommendation, especially since you do not have many hills and no mountains to train on, is to use indoor (hopefully in an air conditioned space) training on a steep treadmill and a stair machine where you may be able to concentrate on longer easier training. I understand the boredom factor but we do work with many clients for whom these are the only options.