First of all FORGET about getting a good phase alignment between fills and delays (or any other 2 sets of speakers that are in physically different places.
Sure, you can get it in ONE seat, but move a few seats to the side and now it all falls apart.
I just want to add some "delay speaker" thoughts that many people don't often address.
And that is consider what is happening COMPLETELY OUT of the coverage pattern of the delay speakers.
Lets say the delays are covering a balcony. Once you have the delay time set, there are other considerations. Freq response and level.
So let's assume you have the response and level "just right" for the balcony.
HOWEVER-what about the seats ON THE MAIN FLOOR?
Unless the delay speaker has a LARGE FULL RANGE horn, there will be spillage onto the main floor.
So now you have screwed up the response there.
And sometimes people on the floor will "hear" the delay speakers and get some sort of "pulling of image" up to them-which makes it harder to enjoy the performance.
SO now comes the "balancing act". I will not go into a lot of details here, but often you have to drop the level of the delay speakers (so they are not heard as loud on the floor).
Sometimes you will have to raise the highpass filter so the lower freq out of the delay are not as loud on the seats below.
Yes the level and response may not be exactly what you want-but now BOTH sections are overall better.
You MUST continue to listen to the different seats in a room whenever you have more than one speaker for the damage the other speakers are doing to the coverage area of the main speaker.
That is why I love the multi mic setup, it allows you to put mics in different places and monitor what is going on all at the same time, so you can actually "see" what effect one speaker has on anothers coverage area.