Keeping my heels down is something I've been struggling for for an extremely long time. This is because my achilles tendons are shortened, so I cannot physically keep a nice low heel. If I stand up in the stirrups, press all my weight down, and brace against the stirrups to sink my heel as low as possible, it barely looks like I'm trying at all. When riding my toes are level with my heels, and I cannot fix that unless I brace against the stirrups.
I have a fairly stable leg with and without stirrups. It's keeping my heels down that is a huge issue. By doing constant stretching I am slowly able to lengthen my tendons so that I'll be able to get my heels lower, but that takes a lot of time (it's a long-term thing, not something that'll be fixed in a day). My question is, how important is it to get my heel down lower? Should I be investing more effort, or perhaps focusing on something else (if so, what)? And if it's that crucial to get my heel down, what are some tips to get a lower heel?