Field Required at Sales Process stage - popup message?

We have a couple of fields that are only required when the opportunity hits a specific sales stage in the sales process. We make them required by setting up the configuration within the sales process set up so there are not validation formulas or anything like that at this point.

With the way we have it right now, if users change the sales stage to that specific one, the other field labels become red in the layout and if the users tries to save the opportunity without entering any data on those, the page refreshed and a very small red "required" text shows right next to each field but there is no popup message at all. Since our layouts are very large, it is difficult to some user to recognize why the record is not being saved without scrolling and looking around.