Changing notification sound for Twitter app

This is a long-standing issue regarding changing iPhone notification sounds for third-party apps - specifically Twitter. As you may already know, the route that takes you from Settings>Notifications>Twitter only lets you toggle 'Sounds' on and off. There is not an option to change the tone and the app defaults to 'Tri-tone' when alerting you to new Tweets, mentions etc. Going via Settings>Sounds and allocating the 'Tweet' sound under the heading 'Tweet' does absolutely nothing on my iPhone - not even when I'm posting to Twitter directly from Photos. I find it extraordinary that we have come so far with the iPhone but there is still no work-around to change a simple notification sound. FYI, I've looked at the settings menu within the Twitter app itself, but their 'Sound effects' setting only allows you to toggle on and off, not change the actual sound. This is a small but continually irritating issue and I was wondering if anyone has worked out any way of resolving this? Likewise, does anyone at Apple have a reason as to why this has never been addressed aside from blaming the app developers? Thanks for your time, Dan.