Indeed, it is a forum wide setting, as it affects all users who cannot hide the “double posts” when they are entered in this way by others.
But this is only a marginal case, I have skimmed your posts from this week and this only seemed to happen once after the new version of Discourse was implemented?
There are a lot of partial quotes in your posts and they are all retained exactly as intended.
Purging is only in effect for the new posts after the recent upgrade, which can be seen in this old reply here, where the quoted two lines take up even more space than the gap between two posts (when seen on mobile) 
I’m sad to hear that the Discourse app is difficult for you to use, but the developers of Discourse are quite friendly and responsive to user input, maybe you could give them some pointers as where to direct their effort.
See replies from the staff members in this topic:
https://meta.discourse.org/t/accessibility-assistive-technology-support/1182/36
I hope they will hear your concerns and make their software even friendlier for you, as I really enjoy all the content and additional features you provide for the entire community here 
