If you could hit at 25, you should have been able to hit at 50, the change is not that great there. Make sure you have your rifle solid though, use bags or something of the sorts. Less movement the better, but if you've sighted in a gun before, and I think you said you're a glass not red dot guy then you know this... I just put a strike fire on a rifle I build for my dad last weekend and it would ring a IPSC steel target at 50 before sighting it in, this has been my experience with most vortex stuff right out of the box. But just bore sight or if you irons that you can use to help do so. Even if you did it on another rifle to get it close enough you can then do your final sighting on the rifle you intend to use (I have a friend who did this and it worked well actually after having issues like you).
But your red dot won't be any different than other scopes you are used to when sighting it in... I would go with a zero at 50, or go about an inch and a half high at 50. This is a dead zero at 200 with 556. And you are still going to be center mass or on target just fine at 100. Then your holds for 3, 4, and 5 are very simple too... For me 50 just works, and I really think it is best. I had a bolt action varmint sighted in at 100 and it was sub MOA but then realized that a zero at 100 doesn't do a whole lot of good for other distances in .223. So just a word of advice here but I hope you get it all worked out!
But your red dot won't be any different than other scopes you are used to when sighting it in... I would go with a zero at 50, or go about an inch and a half high at 50. This is a dead zero at 200 with 556. And you are still going to be center mass or on target just fine at 100. Then your holds for 3, 4, and 5 are very simple too... For me 50 just works, and I really think it is best. I had a bolt action varmint sighted in at 100 and it was sub MOA but then realized that a zero at 100 doesn't do a whole lot of good for other distances in .223. So just a word of advice here but I hope you get it all worked out!